1. Identify the type of chemical reaction
(i) 
(ii) 
Ans. (i) Decomposition reaction
(ii) Double displacement reaction
2. Why does not silver evolve hydrogen on reacting with dil 
Ans. Silver do not evolve hydrogen on reacting with dil. H2SO4 as silver is a less reactive metal than hydrogen.
3. Way do diamond and graphite, the two allotropic forms of carbon evolve different amounts of heat on combustion?
Ans. Diamond and graphite are the two allotropes of carbon but they do not evolve same amount of heat on combustion because they differ in the arrangement of carbon atoms and also their shapes one different.
4. What is the sole of oxidizing agent is a reaction?
Ans. The oxidizing agent supplies the oxygen in a reaction or it removes the hydrogen.
5. What happens chemically when quick lime is added to water?
Ans. When quick lime is added to water calcium hydroxide (slaked lime) is formed with a hissing sound and a lot of heat is evolved during the reaction. The reaction involved is CaO (s) + H2O(Quick Lime) 
Ca (OH) 2 (s) + Heat (Shaked Lime)
6. Why is a combustion reaction an oxidation reaction?
Ans. Combustion reaction because it is always carried out in the presence of air or oxygen for e.g. CH4 (g) + 2O2 (g) 
Co2 (g) +2H2O (l)
7. Why are food particles preferably packed in aluminum foil?
Ans. Aluminum foil does not corrode in the atmosphere even if kept for a long time because a protective coating of aluminum oxide (Al2O3) is formed on the surface of the foil and stops any further reaction of the metal with air and water thus food particles do not get spoiled.
8. What happens to lime water when Co2 gas is bubbled through it in excess?
Ans. When CO2 gas is bubbled through lime water in excess then initially it becomes milky but then its milkiness disappears.
9. Why is a Combustion reaction an oxidation reaction?
Ans. Combustion is an oxidation reaction as it is always carried out in the presence of oxygen.
10. Identify the type of chemical reaction
(i) 
(ii) 
(iii) Combination reaction
Ans. (ii) Displacement reaction
11. Why cannot a chemical change be normally reversed?
Ans. Chemical change cannot be reversed back because products so formed in a chemical reaction are totally different from the reactants.
12. Identify the substance oxidized and reduced in the reaction.
Ans. The substance oxidized is Zinc oxide and the copper oxide gets reduced to copper.
13. A student took 2-3 g of a substance X in a glass beaker & poured water over it slowly. He observed bubbles along with hissing noise. The beaker becomes quite hot. Identify X. What type of reaction is it?
Ans. X = Calcium oxide (Quick lime), Combination reaction.
14. A substance X used for coating iron articles is added to a blue solution of a reddish-brown metal Y, the color of the solution gets discharged Identify X and Y & also the type of reaction.
Ans. X= Fe, Y = Cu, Displacement reaction.
15. A student burnt a metal A found in the form of a ribbon. The ribbon is burnt with a dazzling Flame & a white powder B is formed which is basic in nature. Identify A & B. Write the Balanced chemical equation.
Ans. X = Mg, Y = MgO, Mg + 
16. Why should a magnesium ribbon be cleaned before burning in the air?
Ans. Magnesium ribbon is cleaned before burning to remove the protective layer of basic magnesium carbonate from the surface of the magnesium ribbon.
17. Write the balanced chemical equation with state symbols for the following reactions?
Ans. Balance chemical reaction with state symbols are as follows-
i. BaCl2(aq) + Na2SO4 (aq) BaSO4 (s) + 2NaCl (aq)
ii. NaOH (aq) + HCl (aq) NaCl (aq) + H2O
18. A solution of a substance ‘X’ is used for whitewashing
i. Name the substance ‘X’ and writes its formula.
ii. Write the reaction of the substance ‘X’ named in (i) above with water
Ans. (i). The substance whose solution is water is used for whitewashing is calcium oxide. Its formula is CaO.
(ii). CaO (s) + H2O Ca(OH)2 (s)
19. Which of the following statement about the reaction below are incorrect?
2PbO (s) + C (s) 2Pb (s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidized
(c) Lead oxide is getting oxidized
(d) Lead is getting reduced
i. (a) and (b)
ii. (a) and (c)
iii. (a), (b) and (c)
iv. All
Ans. As statement (a) and (b) are incorrect, answer (i) is correct.
20. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Ans. The reaction involved is:
21. What do you mean by a precipitation reaction? Explain by giving examples.
Ans. A chemical reaction in which an insoluble substance (precipitate) is formed is called precipitation reaction. For example
AgNO3 + NaCl AgCl + NaNO3
22. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Ans. The brown coloured element ‘X‘ is copper. On heating in air it forms copper oxide, which is black in colour.
2CuS + O2 2CuO
23. Why do we apply paint on iron articles?
Ans. We apply paint on iron articles to prevent rusting. Iron articles do not come in contact of atmospheric oxygen and moisture and thus the rusting is prevented.
24. Oil and fat-containing food items are flushed with nitrogen. Why?
Ans. Oil and fat-containing items get rancid due to oxidation with atmospheric oxygen. To prevent rancidity food items are flushed with nitrogen. Nitrogen does not react with oil and fat-containing items.