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D) Displacement

When an iron nail dipped in the copper sulphate solution, iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes. The reaction is:

Fe + CuSO₄ → FeSO₄ + Cu

Different metals react with oxygen at different rates.

e.g., Sodium (Na) and potassium (K) catch fire, if left in open. Hence, these are the most reactive metals. To prevent accidental fires, these metals are kept immersed in kerosene oil. Magnesium burns in air only by heating. So, it is less reactive than sodium and potassium. Copper (Cu) does not burn on heating but blister copper burns. Hence the order of reactivity of these metals with oxygen is : 

Na > Mg > Cu. 

Metals react with water to produce a metal oxide and hydrogen gas. Sodium (Na) and potassium (K) react violently with cold water. So the reaction is violent and exothermic. Magnesium (Mg) does not react with cold water. It reacts with hot water. Metals like lead, copper, silver do not react with water at ail. The reactivity series of metals towards water is : 

Na > Mg > Cu

CuSO₄ + Fe →  FeSO₄ + Cu

CuSO₄ -(Blue)

 FeSO₄  - (Green)

Iron is more reactive than copper. Hence it displaces copper from copper sulphate and due to formation of FeSO₄, the colour changes from blue to green.

Correct option is (b) 0.7 M

From the sets of reactions i, ii, iii, it can be observed from i and ii that X is more reactive than Y and hence it displaces Y from its salt. 

From reaction iii it can be observed that Z is more reactive than X as it displaces X from its salt. 

So the most reactive element is Z and the least reactive is Y. 

So correct answer is d [Z and Y].

(a) The acidic behavior of an acid is due to the presence of hydrogen ions [H⁺ (aq) ions] which are produced only when acids are dissolved in water. In the absence of water, acids do not produce hydrogen ions and hence do not show acidic behavior.

(b) The aqueous solution of an acid conducts electricity due to the presence of charged particles called ‘ions’ in it. These ions carry electric current.

(c) Distilled water does not conduct electricity because it does not contain any ionic compounds dissolved in it whereas rain water does.

Reason: When rain water falls on earth through the atmosphere, it dissolves an acidic gas ‘carbon dioxide’ from the air and forms carbonic acid (H₂CO₃). The carbonic acid provides some hydrogen and carbonate ions to the rain water. Due to the presence of these ions, rain water conducts electricity

Acids don’t show acidic behaviour in the absence of water as H⁺ ions are absent in them.

Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only.

The speed of the reactions is higher in X test tube than Y test tube. 

Reason : 

Due to strong acidic nature, Hydrochloric acid reacts very fast with magnesium ribbon.

Iron nail gets covered with a red-brown coating of copper metal; The blue colour of copper sulphate solution fades gradually.

Blue colour changes to light green. Reddish brown deposit on the iron nail.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

In test-tube B change will be observed because iron is more reactive than copper and it will displace Cu from CuSO₄. 

CuSO₄ + Fe → FeSO₄ + Cu.

1) Take a small amount of calcium hydroxide (base). 

2) Add CO into it. 

3) Salt and water are produced. 

Equation : 

Non-metallic oxide + Base → Salt + Water 

Result: It is a neutralization reaction

We know that hydrochloric acid (HCl) is a strong acid and acetic acid (CH₃COOH) is a weak acid. Being a strong acid, HCI solution contains a much greater amount of hydrogen ions in it. Due to this, the fizzing will occur more vigorously in test tube A. The fizzing is due to the evolution of H₂ gas which is formed by the action of acid on the magnesium ribbon.

Iron is more reactive than copper and hence it can displace only copper from its salt. Iron is less reactive as compared to aluminium or zinc so they will not be displaced from their salts. Also iron will not react with its own salt. So the reddish brown coating on surface of nail is of copper deposition which will be observed only in case of iron nail dipped in copper sulphate solution. 

So the correct answer is c.

(i) Solution D

(ii) Solution C

(iii) Solution B

(iv) Solution A

(v) Solution E

Increasing order C,E,D,A,B

a) Neutral ➝ solution D ➝ pH value of pH is 7.
b) strongly alkaline ➝ solution C ➝ pH is 11
c) strongly acidic ➝ solution B ➝ pH is 1
d) weakly acidic ➝ solution A ➝ pH is 4
e) weakly alkaline ➝ solution E ➝ pH is 9
We can arrange the pH in increasing order of hydrogen ion concentration as 11 < 9 < 7 < 4 < 1

Arrangement of the pH in increasing order of hydrogen ion concentration is as follows:

11 < 9 < 7 < 4 < 1

Correct option is: B) Hydrochloric acid and sodium hydroxide

Correct option is: C) antacid

Solution – pH Value 

A → 4 

B → 1 

C → 11 

D → 7 

E → 9 

a) Solution ‘D’ is neutral 

b) Solution ‘C’ is strongly alkaline

c) Solution ‘B’ is strongly acidic 

d) Solution ‘A’ is weakly acidic 

e) Solution ‘E1 is weakly alkaline 

∴ Increasing order of Hydrogen ion concentration : 

C < E < D < A < B

Correct option is: D) Red

False

The universal indicator shows different colours at different concentrations of hydrogen ions in a solution.

Substances having pH values above 7: Solution of washing soda and toothpaste; They will turn red litmus paper blue due to their basic nature.

Substances having pH values less than 7: Lemon juice, vinegar and stomach juices; They will turn blue litmus paper red due to their acidic nature.

Litmus is a common acid-base indicator. It is not a universal indicator.

These solutions can be tested by using universal indicators. If the solution (i) turns red it is an acid and If the solution (ii) remains colourless it is a base.

The answer is (c) Vanilla essence

Vanilla essence can be used as an olfactory indicator hence it can be used as acid base indicator by visually impaired students

1. The volatility of acetic acid (CH₃COOH) is more than that of hydrochloric acid. 

2. But HCl solution has more strength than acetic acid. 

3. Hence magnesium ribbon in test tube A will react more vigorously than in B.

4. So fizzing occurs more vigorously in test tube ‘A’.

Correct option is c. 128

Option : (c) HClO₂ < HClO₃ < HClO₄

Answer: (d) BeCO₃

The water vapour present in the air comes in contact with the glass containing ice-cold water. The vapour loses its energy to the cold water and gets converted to water droplets which we see on the outer surface of the glass. This process is called condensation

The humidity (amount of water vapour present in the air) is low on a dry day. Being a hot dry day, the temperature is high and the humidity is low. The rate of evaporation increases with

i. increase in temperature

ii. decrease in humidity

Therefore the rate of evaporation and hence the cooling effect due to evaporation is high on a hot dry day. Thus, desert cooler cools better on a hot dry day.

We perspire more in summer. Sweat present in the surface of our body absorbs the energy equal to the latent heat of vapourisation and gets converted to vapour. This gives a cooling effect to our body. This is called evaporative cooling. Cotton is a good absorber of water. Hence, cotton clothes absorb the sweat and expose it to the surroundings for easy evaporation.

We should wear cotton clothes in summers. During summers, we sweat more. On the other hand, cotton is a good absorber of water. Thus, it absorbs sweat from our body and exposes the liquid to the atmosphere, making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.

We should wear cotton clothes in summer to keep cool and comfortable as cotton is good absorber of water, so it absorbs the sweat from our body and exposes it to air for evaporation of sweat thus cools our body.

(a) 293 K

293K – 273K

= 20° C

(b) 470 K

470 K – 273 K

= 197° C.

During summer we should wear cotton clothes because cotton absorbs heat quickly and evaporate and helps to cool our body.

The surface area of a saucer is greater than that of a cup. It is to be noted that the rate of evaporation increases with an increase in surface area. This is because, as the surface area is increased, more particles in the surface are exposed to the surroundings and hence more particles would get converted into a vapour phase by acquiring energy from surroundings.

Because in a saucer, the surface is broad comparing to cup and here rate of evaporation is greater. Hence we are able to sip hot tea or milk faster from a saucer rather than a cup.

B) latent heat of vapourisation

(a) Round shaped : Basket ball, orange, globe, apple and earthen pitcher
     Other shapes : Water and sugar
(b) Eatables : Water, orange, sugar and apple
     Non eatables : Basket ball, globe and earthen pitcher

Burns caused by the steam is much more severe than boiling water because: 

i. Water vapour (steam) at 373k (100°C – boiling point) have more energy than the boiling water at the same temperature. 

ii. Particles in steam have absorbed extra energy in the form of latent heat of vaporization. 

iii. Hence, due to this extra energy, steam causes more burns than boiling water.

1. Steam particles have more energy than the particles of boiling water. 

2. This is because particles in water vapour have absorbed additional energy in the form of latent heat of vaporization. 

3. So, steam produces more severe burns than boiling water.

The factors which affect the rate of evaporation are:

(1) Surface area: 

Evaporation is a surface phenomenon. As the surface area increases, more particles present in the liquid surface are exposed to the surroundings, and the rate of evaporation also increases.

(2) Temperature:

With the increase in temperature, more particles are provided with kinetic energy to escape into the vapour state. Hence the rate of evaporation increases.

(3) Humidity:

Humidity is the amount of water vapour present in the air. For a given temperature, the air can only hold a particular amount of water vapour. So if the humidity is high, the amount of water vapour is high and hence the further conversion of a liquid into a vapour state is difficult or not favourable. Hence the rate of evaporation decreases.

(4) Wind Speed: Increase in wind speed results in more moving away from water vapour particles with the wind, decreasing the amount of water vapour present in the air in that area. So the rate of evaporation increases with the wind speed.

Books, notebooks, newspaper, toys, calenders etc.

1. green 

2. Synthetic indicator. 

3. red, yellow 

4. pink, does not change 

5. olfactoryin dicators. 

6. Universal indicatoris 

7.  Universal indicator 

8. pH 

9. less than 7 

10. more than 7 

11. 7 

12. weak 

13. hydrogengas. 

14. calcium carbonate 

15. neutralization reaction. 

16. water, salt 

17. bases. 

18. formic 

19. quick lime/ potassium hydroxide. 

20. compost. 

21. Acid rain. 

22. Acetic 

23. Tannic 

24. Ammonium hydroxide 

25. antacid and laxative