Question

Which metal forms hydrogen gas when react with cold water?

• A. $\mathrm{Na}$
• B. $\mathrm{Mg}$
• C. $\mathrm{Fe}$
• D. $\mathrm{Zn}$

Answer 1

The correct option is A

$\mathrm{Na}$

Alkali metals react vigorously with cold water and liberated Hydrogen ($H_2$) gas.

Explanation for correct option:

(A) Sodium($\mathrm{Na}$) reacts with cold water vigorously to form sodium hydroxide ($\mathrm{NaOH}$) and ${\mathrm{H}}_2$gas.

$\underset{\mathrm{Sodium}}{2\mathrm{Na}\left(\mathrm{s}\right)}+\underset{\mathrm{Cold}\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Explanation for incorrect options:

(B) Magnesium($\mathrm{Mg}$) reacts with cold water very slowly instead it reacts rapidly with boiling water.

(C) Iron($\mathrm{Fe}$) only reacts when steam is passed over red hot iron($\mathrm{Fe}$).

(D) Zinc($\mathrm{Zn}$) only reacts with steam.

Therefore, the correct option is (A).