Which of the following combinations will produce H 2 gas?

Which of the following combinations will produce H2 gas?
  1. Zn metal and NaOHaq
  2. Au metal and NaCNaq in the presence of air
  3. Cu metal and conc. HNO3
  4. Fe metal and conc. HNO3

Solution

(i)  Zn+2NaOH→Na2ZnO2+H2
(ii) 4Au+8NaCN+O2+2H2O→4NaAuCN2+ 4NaOH
(iii)  C⁡ u⁡ + 4 H⁡ N⁡ O⁡ 3 → C⁡ u⁡ N⁡ O⁡ 3 2 + 2 N⁡ O⁡ 2 +  2 H⁡ 2 O⁡ conc.
(iv) Formation of passive layer of Fe2O3 on the surface of Fe and NO2 gas is evolved.
Fe+4HN O 3 →Fe ( N O 3 ) 3 +N O 2 + 1 2 O 2 :

Asked in: JEE Advanced 2017 (Paper 2)

Practice more Hydrogen questions on Aicharya