Question

Which of these given reactions is identified as a gas evolving reaction?

• A. Reaction of zinc and sulphuric acid
• B. Reaction of sodium hydroxide and sulphuric acid
• C. Reaction of potassium iodide and lead nitrate
• D. Reaction of quick lime and water

Answer 1

The correct option is A Reaction of zinc and sulphuric acid

When zinc is added to sulphuric acid, hydrogen gas evolves. The reaction results in formation of zinc sulphate and hydrogen gas which is a characteristic of evolution of gas.
$Zn+H_{2}S{O}_4\left(dil\right)\to ZnS{O}_4+H_2$

Reaction of sodium hydroxide with sulphuric acid gives sodium sulphate and water, which is called a neutralisation reaction. Hence no gas is evolved.
$2NaOH+H_{2}S{O}_4\to N{a}_{2}S{O}_4+2H_{2}O$

Lead iodide precipitates when potassium iodide reacts with lead nitrate. There is no evolution of gas.
$2KI\left(s\right)+Pb\left(N{O}_3{)}_2\right(s)\to 2KN{O}_3(aq)+Pb{I}_2(s)$

When water is added to quick lime,slaked lime is formed and no gas is evolved. $CaO+H_{2}O\to Ca(OH{)}_2$