(a) A substance X, an oxide of a metal, is used extensively in the cement industry. This element is found in our bones also. One treatment with water it forms a solution which turns red litmus blue.

Identity X and also write the chemical reaction involved.

(b) Choose a metal from the following metals which reacts only with hot water: Sodium, magnesium, iron.

Mention the products formed during the reaction. (2014)

State the kind of chemical reactions in the following examples: (2014)

(i) Digestion of food in stomach

(ii) Combustion of coal in air

(iii) Heating of limestone

Write the balanced chemical equation for the following reaction: (2014)

(i) Phosphorus burns in chlorine to form phosphorus pentachloride.

(ii) Burning of natural gas.

(iii) The process of respiration.

Name the substance oxidised and the substance reduced, and also identify the oxidising agent and reducing agents in the following reaction:

(a) 3MnO₂ + 4Al → 3Mn + 2Al₂O₃

(b) Fe₂O₃ + 3CO → 2Fe + 3CO₂

(c) SO₂ + 2H₂S → 3S + 2H₂O (2015)

(a) In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?

(b) (i) What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?

(ii) What type of reaction is this?

(iii) Write a balanced chemical equation to represent the above reaction. (2015)