Look at the following figure and answer the questions that follow:

(a) Which gas is prepared by this method marked as A.

(b) Name this method of collection. Why is this method used?

(c) Why is nitric acid not used as a reactant in the above method?

(d) Conc. H₂SO₄ is a good drying agent. However, it is not used here. Why?

(a) Hydrogen

(b) Downward displacement of water.

This method is used as:

1. Hydrogen is virtually insoluble in water (20 ml of hydrogen dissolves in 1 litre of water under normal conditions)
2. Hydrogen forms an explosive mixture with air and therefore, cannot be collected by downward displacement of air even though it is lighter than air.

(c) Nitric acid, even in its dilute form, is not used in the preparation of hydrogen from metals because it is a powerful oxidizing agent, and the oxygen formed due to its decomposition oxidizes the hydrogen to give water, thus defeating the purpose of the reaction.
3Zn + 8HNO₃ ⟶ 3Zn(NO₃)₂ + 4H₂O + 2NO↑

(d) Conc. H₂SO₄ is a good drying agent. However, it is not used to dry hydrogen as it reacts with hydrogen, thus defeating the purpose of the reaction.
H₂SO₄ + H₂ ⟶ 2H₂O + SO₂