Question

Which of the following pair will not evolve Hydrogen gas?
a. zinc and sodium hydroxide
b. iron and steam
c. copper and dilute hydrochloric acid
d. granulated zinc and dilute hydrochloric acid ​

Answer 1

Answer:

Copper rs a noble metal. as it lies below hydrogen in the electrochemical series. Therefore it can't displace hydrogen from dilute HCl.

Answer 2

Answer :-

(c). Copper and dilute Hydrochloric acid .

Explanation :-

In order to solve this question, firstly we should know the reactivity series from Potassium (most reactive) and upto Platinum (least reactive) . Generally elements placed above Hydrogen in the reactivity series are more reactive and below it are less reactive.

Here, all metals are placed above hydrogen except Copper . Also, copper is a metal that doesn't reacts with dil. hydrochloric acid. So it is the required answer.

The balanced equations are :-

(a) Zn + 2NaOH → Na₂ZnO₂ + H₂

(b) 3Fe + 4H₂O → Fe₃O₄ + 4H₂

(c) Cu + HCl → No reaction

(d) Zn + 2HCl → ZnCl₂ + H₂