Cls 10 Sci Chp 10. Solsn

Class 10 Science Solutions 

Chapter 10 Light - Reflection and Refraction

Page: 168

1. Define the principal focus of a concave mirror.

Ans:

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is called the principal focus of the concave mirror.

2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Ans:

Radius of curvature (R) = 20 cm

Radius of curvature of the spherical mirror = 2 × Focal length (f)

R = 2f

f= R/2 = 20 / 2 = 10

Therefore, the focal length of the spherical mirror is 10 cm.

3. Name the mirror that can give an erect and enlarged image of an object.

Ans: Concave Mirror.

4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Ans:

Convex mirrors always form an erect, virtual, and diminished image of the objects placed in front of it.

Page No: 171

1. Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Ans:

Radius of curvature (R) = 32 cm

Radius of curvature = 2 × Focal length (f)

R= 2f

f = R/2 = 32/2 = 16

Therefore, the focal length of the given convex mirror is 16 cm.

2. concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located ?

Ans:

Because the image is real, so magnification m must be negative.

Thus the image is located at a distance of 30 cm from the mirror on the object side of the mirror.

Cls 6 Sci Chp 4 Notes

 Class 6 Science Notes 

 Chapter 4 Sorting Materials Into Groups 

Object Around Us

→ Objects are made up of one or more materials.

→ One material can be used to make different type of objects.

→ It may be man-made or naturally occurring.

→ Material is a substance which is used to make different objects.

Properties of materials

→ Material occupy space.

→ Materials have mass.

• Material can be classified on the basis of physical state as:

(i) Solid

Examples:  sand, steel and stone.

(ii) Liquid

Examples:  oil, water and milk.

(iii) Gas

Examples: steam, nitrogen and oxygen.

General properties of material

Appearance

→ Lustrous (all metals are lustrous, some are more and some are less).

→ Non-lustrous (wood, rubber and piece of rock)

Hardness (Hard and soft)

→ Brittle (break into small pieces or become powdered when hammered.

Eg: - glass and salt)

→ Malleable (spread into sheets when beaten. Metal are malleable

→ Ductile ( which can draw into thin and long wire)

Visibility

→ Transparent (Materials that allow the entire light pass through it, like glass, water etc.)

→ Translucent (Materials that allow some light to pass through it, like coloured glass, oiled paper.)

→ Opaque (The material which do not allow light to pass through it, like stone, wood etc.)

Electricity

→ Good conductor (Metals are good conductor ; electricity can pass through it)→ Bad conductor (non-metals ; electricity can’t pass through it)

Heat

→ Good conductor (metals are good conductor)

→ Bad conductor (non-metals are bad conductor)

Materials may float and can sink in water

→ Material which sinks in water is denser than water

→ Material which floats on water is less dense than water.

Solubility of a substance in water

→ The substance like salt and sugar which disappear in water are called as soluble.

→ The substances which don’t disappear in water are known as insoluble in water

Miscible and immiscible liquid

→ When two liquid mixed and they do not mixed well is known as immiscible.

→ The liquids which mix well with water are said to be miscible.

Solute, solvent and solution?

→ The substances which dissolve in water are called solute.

→ A solvent is a substance that dissolves the solute to make the solution.

→ The mixture of solute and solvent is called solution.

How are material grouped

• The materials which are similar in one or two ways can be put in one group.

→ Things made from wood.

→ Things made from fibre.

→ Things made from metal.

→ Things made from ceramic.

→ Things made from glass.

→ Things made from plastic.

→ Things made from rubber.

→ Things that are liquids such as oil.

Advantages of classification

→ Helps in identifications of objects.

→ Helps in sorting of objects.

→ Helps in locating things.

→ Makes study of different objects easy and more meaningful rather than studying each other separately.

→ Helps to understand similarities and dissimilarities among objects.

Cls 6 Sci Chp 3 notes

 Class 6 Science Notes 

 Chapter 3 Fibre to Fabric 

Fibres

→ Fibre is a fine thread-like filament.

→ Fabric is made up of threads of yarns arranged together.

There are two types of fibre:

(i) Natural fibre

(ii) Synthetic fibre

Natural fibres

→ The fibre which are obtained from plants and animals is known as Natural fibre.Examples: cotton, jute, silk and wool.

→ Cotton and jute are obtained from plants while wool and silk are obtained from animals.

→ Silk fibre is drawn from the cocoon of silkworm and wool is obtained from the fleece of sheep or goat, it is also obtained from the hair of rabbits, yak and camels.

Synthetic fibres

→ Fibres which is made by man from chemical substance is called synthetic fibres.

Examples: rayon, nylon, polyester etc.

Variety of Natural Fibre

→ Natural fibres are obtained from two sources. They are Plant fibre and Animal fibre.

Plant fibre

→ The fibre which are obtained from plant are known as Plant fibre.Examples: Cotton, Jute etc.

• Cotton

→ The plants of cotton are usually grown at the places having black soil and warm climate.

→ Cotton grows in Gujarat, Maharashtra, Punjab, Tamil Nadu, Odisha etc.

→ The fruit of cotton is known as cotton bolls.

→ From the bolls, cotton is usually picked by hand.

→ Ginning is the process of separating cotton fibres from the seeds by combing. It was traditionally done by hands, now machines are available for ginning.

• Jute

→ Jute is used for making of bags and ropes mats etc.

→ Jute fibre is obtained from stem of the jute plant.

→ The cultivation of jute is in rainy season.

→ The cultivation of jute is in west Bengal, Bihar and Assam.

→ When the jute plant is in flowering stage the harvesting is take place.

→ The stems of the jute plant are immersed in water for a few days which then rot and fibres are separated by hand and this process is called stripping.

→ Then the stripped fibres are washed and dried in sun.

Animal fibre

•Wool

→ Wool cloth is spun from yarn made from the fibres of the thick fleece of sheep.

Processing of wool

→ The first step is shearing in which the fleece of the sheep along with thin layer of skin is removed from its body.

→ Then the damaged wool is separate from fleece this process is known as grading.

→ Then these wools are passes through a roller after washing and drying this process is called as carding.

→ In last step spinning is takes place in which fibres are gathered together and drawn into a long rope and then twisted to make yarn.

• Silk:

Silk thread is obtained from the saliva of an insect called silkworm.

Spinning cotton yarn

→ Fabrics are made from yarns, which in turn are made from fibres.

→ The process of making yarn from raw fibrous materials is called spinning.

→ In this process, the fibres are twisted to make yarn.

→ Making fabric from yarn is done by two processes:

(i) Weaving:

It is a process in which the two sets of yarn arranged together to make a fabric is called weaving. It is done by looms.

(ii) Knitting:  The process by which a single yarn is used to make fabric. It is done by hand or by help of machines.

History of clothing material

→ Ancient people used the bark and big leaves of tree or animals skins or furs to cover themselves.

→ After settling in agriculture communities, they learnt to weave twigs and grass into mats and baskets.

→ Early Indians wore fabrics made out of cotton.

→ In ancient Egypt, cotton as well as flax was used for making fabrics.

→ After the invention of the sewing needle, people started stitching fabrics to make cloth. 

Cls 6 Sci Chp 2 Notes

 Class 6 Science Notes 

 Chapter 2 Components of Food 

What are Nutrients?

→ The food that we eat consists of different nutrients or components.

→ The components of food which are needed by our body is  as nutrient.

→ There are six main components present in food:Carbohydrates, fats, proteins, vitamins, minerals and fibers.

→ These components fulfill the different needs of the body.

Carbohydrates

→ Carbohydrates are the compound which is made up of three elements:-Carbon, Hydrogen and Oxygen

→ Carbohydrate provides energy to our body, which keeps it going throughout the day.

→ The main carbohydrates found in our food are in the form of sugars and starch. If food contains starch we can easily test it.

→ The sources of carbohydrates include cereals such as wheat, maize, rice, jawar, bajra, potatoes, bread etc.

→ We can test the presence of carbohydrates by iodine test.

Test for carbohydrates:

Step 1: Take the food item in the test tube and add 2-3 drops of dilute iodine solution to it.

Step 2: After some time if the colour changes to blue-black, it indicates the presence of starch in the food item.

Proteins

→ Proteins are the complex compounds made up of carbon, hydrogen, oxygen, nitrogen and sulphur.

→ The sources of proteins are: cheese, egg, soya bean, pulses, meat etc.

→ Protein is known as body-building food.

Test for proteins:

Step 1: Take food item in the test tube and Add 10 drops of water to it and mix well.

Step 2: Now add 2 drops of copper sulphate and ten drops of caustic soda (sodium hydroxide) solution.

Step 3: Mix it well and keep it undisturbed for some time.

Step 4: After some time you observe the development of violet color in the test tube, it indicates the presence or the proteins.

Fat

→ Fat also provides energy to our body. Fat gives more energy as compared to carbohydrates.

→ Some sources of fat are oil, ghee, egg yolk, milk, butter etc.

Test for fats:

Step 1: Take some food item in a paper and wrap it.

Step 2: Then try to crush it taking care that the paper is not torn.

Step 3: After that take out the food item and allow the paper to be dried for some time.

Step 4: If you can find the oil spots on the paper it indicates the presence of fats in the food item.

Vitamins

→ Vitamins are a group of organic compound which is essential in small amounts for maintaining normal health and development.

→ Vitamins help in protecting our body against diseases. It helps in keeping our eyes, bones, teeth and gums healthy.

→ There are two types of vitamins some are fat soluble and some are water soluble.

→ Vitamins are of different types: - vitamin A, vitamin C, vitamin D, vitamin E, and vitamin K.

→ There are some other vitamins known as vitamin B complex which contain vitamin B1, vitamin B2, vitamin B3, vitamin B5, vitamin B6, vitamin B7, vitamin B9 and vitamin B12.

Minerals

→ Minerals perform important functions such as formation of bones, teeth and blood cell and also maintain the normal heartbeat.

Roughage

→ Roughage is also called dietary fibers.

→ It consist of indigestible plant carbohydrates called cellulose.

→ The source of Roughage is fresh fruits, whole grains and pulses.

Balance diet

→ Our diet should have all the required nutrients in right proportions this should also contain some water and dietary fibers this kind of diet is called as Balanced diet.

→ Balance diet is important for growth and maintenance of good health,

→ It can be very harmful for us to eat too much of fat rich foods and we may end up suffering from a condition called obesity.

Deficiency Diseases

→ Diseases that occur due to lack of nutrients over a long period are called as deficiency diseases.

→ If we do not take a particular nutrient over a long period of time, we suffer from its deficiency.

• Lack of iodine quantity in our body causes Goiter.

• Lack of calcium cause the deficiency bone and tooth decay

• Vitamin A deficiency cause loss of vision

• Vitamin D deficiency cause Rickets

• Lack of iron causes Anemia. 

Cls 6 Nots Chp 1 food

 Class 6 Science Notes  

 Chapter 1 Food Where Does It Come From 

What is food, Variety of food, Ingredients of food?

→ Food is source of nutrition that living organisms eat, drink or absorb to maintain life and growth.

→ There are many different places where we buy food like markets, shop, supermarkets etc.

→ We eat different variety of foods like fish, rice, bread, vegetables meat etc.

Food ingredients

→ Ingredients are the materials used for making food item.

Examples: - The ingredient of rice is water and raw riceThe ingredient of dal is raw dal, spices and water

Use of food in our body

Food in our body is used for various reasons.They are:

(i) For energy

(ii) For work

(iii) For body function

(iv) For good health

(v) For wound healing.

Sources of the food

→ There are two main sources of food:

(a) Plants

(b) Animals

There are many different types of foods that come from animals:

→ Eggs come from chicken.

→ Cows, goat and buffaloes are some common animals which gives us milk and milk products like butter, cream, cheese and curd.

→ Bacon come from a pig.

→ Honey is made by bees, Honey bee collects fruit juices (nectar) from flowers and stores in their hive.

→ Fish cakes are made from fish.

There are many different types of foods that come from Plants:

→ Roots as food: - Carrot, Beetroot, Radish, Turnip, etc.

→ Stem as food: - Potato, Ginger, Sugarcane.

→ Leaves as food: - Spinach, Coriander, Cabbage, Onion etc.

→ Flowers as food: - Rose, Cauliflower, Bauhinia etc.

→ Fruits as food: - Apple, Banana, Tomato, Grapes etc.

→ Seeds as food: - Corn, Wheat, Maize, Pulses etc.

• Some plants have two or more edible parts: - mustard seeds give us oil and its leaves are also used as vegetable.

Classification of animal based on food they eat

Herbivores

→ Animals which eat only plants or plant products as their food are called as Herbivores.

→ Herbivores animals have sharp teeth for biting and cutting, and very strong teeth for grinding as plant food needs to be chewed a lot as it is very rich in a substance called cellulose.

→ Examples: Cow, goat, horse etc.

Carnivores

→ Animals which eat the flesh of other animals are called carnivores.

→ Most of the carnivorous animals have very sharp teeth for tearing out the flesh of its prey.

→ Examples: Lion, tiger, snake and lizard (it eats insects i.e., other animals)

Omnivores

→ Animals which eat both plants and animals are called omnivores.

→Examples: Dog, man.

Cls 10 Sci Chp 5 Soluns

Class 10 Science Solution

Chapter 5 Periodic Classification Of Elements 

Intext Questions 

Page Number: 81

1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves ? Compare and find out.

Ans:

Yes, Dobereiner’s triads also existed in the columns of Newland’s Octaves.

For example, Li, Na, K.

If we consider lithium (Li) as the first element, then sodium (Na) is eighth element. If we consider sodium as the first element, then potassium is the eighth element.

2. What were the limitations of Dobereiner’s classification ?

Ans:

> It failed to arrange all the then known elements

> Dobereiner could identify only three triads from the elements known that time.

3. What were the limitations of Newlands’ law of octaves ?

Ans:

(i) Newlands law of octaves was applicable to the classification of elements upto calcium only. 

(ii) Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in the future. 

Page Number: 85

1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements : K, C, Al, Si, Ba

Ans:

K2O, CO2, Al2O3, SiO2, BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table ? (any two)

Ans:

Scandium and Germanium.

3. What were the criteria used by Mendeleev in creating his Periodic Table ?

Ans:

Mendeleev used atomic mass to arranged the elements in periodic table.

4. Why do you think the noble gases are placed in a separate group ?

Ans:

Similar inert behaviour and similar electronic configuration, they are justified to be placed in a separate group.

Page Number: 90

1. How could the modern periodic table remove various anomalies of Mendeleev’s periodic Table ?

Ans:

(i) The modern periodic table is based on atomic number, while Mendeleev’s periodic table was based on atomic mass.

(ii) The isotopes of an element have same number of protons (or atomic number). So they are alloted the same position in modern periodic table.

(iii) Cobalt and nickel are placed at 9th and 10th position respectively.

(iv) Hydrogen has been alloted special position, i.e., it is placed at the top of alkali metals in the first group.

2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Ans:

Calcium and Beryllium are similar to Magnesium because all the three elements belong to the same group and have 2 valence electrons in their outer shell.

3. Name

(a) Three elements that have a single electron in their outermost shells.

(b) Two elements that have two electrons in their outermost shells.

(c) Three elements with filled outermost shells

Ans:

Lithium (Li), Sodium (Na) and potassium (k) have a single electron in their outermost shells.

Magnesium (Mg) and Calcium (Ca) have two electrons in their outermost shells

Neon (Ne), Argon (Ar and Xenon (Xe) filled outermost shells

4. a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Ans:

a) They’ve one valence electron in their outermost shells and as a result of this, they are very unstable. So, they readily react with water to liberate hydrogen. They are also called alkali metals.

b) Their outermost shells are full leading to high stability. They react only in extreme circumstances and hence are called noble gases.

5. In the Modern Periodic Table, which are the metals among the first ten elements?

Ans:

Lithium and Beryllium are the metals among the first ten elements in Modern Periodic Table.

6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic? Ga Ge As Se Be

Ans:

Among the elements listed in the question. Be and Ga are expected to be most metallic. Out of Be and Ga, Ga is bigger in size and hence has a greater tendency to lose electrons than Be. Therefore, Ga is more metallic than Be.

Exercise questions 

1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Periodic Table.

(a) The elements become less metallic in nature.

(b) The number of valence electrons increases.

c) The atoms lose their electrons more easily.

(d) The oxides become more acidic

Ans: c) The atoms lose their electrons more easily.

2. Element X forms a chloride with the formula XCl2, which is solid with a high melting point. X would most likely to be in the same group of the periodic table as

(a) Na       (b) Mg      c) Al       (d) Si

Ans:   (b) Mg

3. Which element has

(a) two shells, both of which are completely filled with electrons ?

(b) the electronic configuration 2, 8, 2 ?

c) a total of three shells, with four electrons in its valence shell ?

(d) a total of two shells with three electrons in its valence shell. v

(e) twice as many electrons in its second shell as in its first shell ?

Ans:

(a) Neon (2, 8)

(b) Magnesium

(c) Silicon (2, 8, 4)

(d) Boron (2, 3)

(e) Carbon (2, 4)

4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Ans:

(a) Valency equal to 3.

(b) Valency equal to 1.

5. An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)N(7) F(9) P(15) Ar(18)

Ans:

(a) The atomic number of this element is 17.

(b) It would be chemically similar to F(9) with configuration as 2, 7.

6. The position of three elements A, B and C in the Periodic Table are shown below–

Group 16        Group 17

       –                               –

       –                              A

       –                              –

      B                               C

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A?

Ans:

a) Element A is a non-metal

b) Element C is less reactive than Element A

c) C is smaller in size than B

d) A will form anion

7. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Ans:

Nitrogen (7): 2, 5

Phosphorus (15): 2, 8, 5

Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.

8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Ans:

The number of valence electrons decides an atom’s position in the periodic table while the electronic configuration decides the number of valence electrons.

9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?

Ans:

The element with atomic number 12 has same chemical properties as that of calcium. This is because both of them have same number of valence electrons (2).

10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.

Ans:

Mendeleev’s Periodic Table:

> Elements are arranged in the increasing order of their atomic masses.

> There are 8 groups

> Each groups are subdivided into sub group ‘a’ and ‘b’

> There is no place for noble gases.

> There was no place for isotopes.

Modern Periodic Table:

> Elements are arranged in the increasing order of their atomic numbers.

> There are 18 groups

> Groups are not subdivided into sub-groups.

> A separate group is meant for noble gases.

> Isotope are kept at the same place because their atomic number is same.

Cls 10 Sci Chp 2 MCQ

  Class 10 Science    

  Chapter 2 Acids, Bases and Salts   

  Multiple Choice Questions   

1. Which Acid is present in Tomato?

(A) Citric Acid

(B) Oxalic Acid       

(C) Lactic Acid

(D) HCl

Ans: (B) Oxalic Acid

2. Which Acid is a strong Acid in the following?

(A) HCl pH 1

(B) CH3COOH pH 5   

(C) Lemon juice pH 2.2

(D) Pure Milk pH 6

Ans: (A) HCl pH 1

3. Na2CO3.10H2O is known as-

(A) Baking Soda

(B) Baking Powder

(C) Washing Soda

(D) Bleaching Powder

Ans: (C) Washing Soda  

4. Which salt is Neutral salt?

(A) NH4Cl       

(B) CH3COONH4

(C) CH3COONa

(D) Na2CO3

Ans: (B) CH3COONH4

5. pH value less than 7 indicates that the solution is –

(A) Acidic

(B) Basic

(C) Neutral

(D) No effect

Ans: (A) Acidic

6. Lactic Acid is present in-

(A) Orange

(B) Tea

(C) Curd

(D) Vinegar

Ans: (C) Curd

7. Farmers neutralize the effect of Acidity on soil by adding

(A) Slaked Lime 

 (B) Gypsum

(C) Caustic Soda

(D) Baking Soda

Ans: (A) Slaked Lime

8. CuSO4.5H2O In this Compound the water molecule is called –

(A) Pure Water

(B) Water of Crystallisation

(C) Soda Water

(D) None of these

Ans: (B)Water of Crystallisation

9. In which pH range does our body work to survive in the atmosphere?

(A) 5.5 to 8.5

(B) 7.0 to 7.8

(C) 2.3 to 7.0

(D) 7.5 to 12.5

Ans: (B) 7.0 to 7.8

10. What is the chemical formula of POP (Plaster of Paris)?

(A) CaSO4.2H2O

(B) CaSO4.3H2O

(C) CaSO4.1/2H2O

(D) CaCO3.1/2H2

Ans: (C) CaSO4.1/2H2O

11. Which salt is Acidic in nature?

(A) NH4Cl

(B) CH3COONH4

(C) NaCl

(D)Na2CO3

Ans: (A) NH4Cl

12. When a base reacts with a metal, it forms a salt and hydrogen gas is released. By what method can the presence of hydrogen be detected?

(A) by water

(B) by litmus paper

(C) by methyl orange

(D) by a burning candle

Ans: (D) by a burning candle

13. The image shows the pH values of four solutions on a pH scale.

Which solutions are alkaline in nature?

(A) A and B   

(B) B and C

(C) C and D

(D) A and D

Ans: (C) C and D

14. At what temperature is gypsum heated to form Plaster of Paris?

(A) 35°C      (B) 70°C

(C) 80°C      (D) 100°C

Ans: (D) 100°C

15. Sodium carbonate reacts with hydrochloric acid produces

(A) NaCl

(B) CO2

(C) H2O

(D) All of the above

Ans: (D) All of the above

16. Which Acid is present in Tamarind?

(A) Tartaric acid

(B) Oxalic Acid

(C) Lactic Acid

(D) Citric Acid

Ans: (A)Tartaric acacid

17. In terms of acidic strength, which one of the following is in the correct increasing order?

(A) Water < Acetic acid < Hydrochloric acid

(B) Water < Hydrochloric acid < Acetic acid

(C) Acetic acid < Water < Hydrochloric acid

(D) Hydrochloric acid < Water < Acetic acid

Ans: (A) Water < Acetic acid < Hydrochloric acid

18. What is formed when zinc reacts with sodium hydroxide?

(A) Zinc hydroxide and sodium

(B) Sodium zincate and hydrogen gas

(C) Sodium zinc-oxide and hydrogen gas

(D) Sodium zincate and water

Ans: (B) Sodium zincate and hydrogen gas

19. Brine is an

(A) aqueous solution of sodium hydroxide

(B) aqueous solution of sodium carbonate

(C) aqueous solution of sodium chloride

(D) aqueous solution of sodium bicarbonate

Ans: (C) aqueous solution of sodium chloride

20. Sodium carbonate is a basic salt because it is a salt of a

(A) strong acid and strong base

(B) weak acid and weak base

(C) strong acid and weak base

(D) weak acid and strong base

Ans: (D) weak acid and strong base

21. Alkalis are

(A) acids, which are soluble in water

(B) acids, which are insoluble in water

(C) bases, which are insoluble in water

(D) bases, which are soluble in water

Ans: (D) bases, which are soluble in water

22. Which of the following statements is correct about an aqueous solution of an acid and of a base?

(i) Higher the pH, stronger the acid

(ii) Higher the pH, weaker the acid

(in) Lower the pH, stronger the base

(iv) Lower the pH, weaker the base

(A) (i) and (iii) (B) (ii) and (iii)

(C) (i) and (iv) (D) (ii) and (iv)

Ans: (D) (ii) and (iv)

23. Lime water reacts with chlorine to give

(A) bleaching powder

(B) baking powder

(C) baking soda

(D) washing soda

Ans: (A) bleaching powder

24. Nettle sting is a natural source of which acid?

(A) Methanoic acid

(B) Lactic acid

(C) Citric acid

(D) Tartaric acid

Ans: (A) Methanoic acid

25. Tooth enamel is made up of

(A) calcium phosphate

(B) calcium carbonate

(C) calcium oxide

(D) potassium

Ans: (A) calcium phosphate

26. Rain is called acid rain when its:

(A) pH falls below 7

(B) pH falls below 6

(C) pH falls below 5.6

(D) pH is above 7

Ans: (C) pH falls below 5.6   

27. Sodium hydroxide is a

(A) weak base

(B) weak acid

(C) strong base

(D) strong acid

Ans: (C) strong base

28. When copper oxide and dilute hydrochloric acid react, colour changes to

(A) white

(B) bluish-green

(C) blue-black

(D) black

Ans: (B) bluish-green