Question

The metal that reacts with cold water is

• A. mercury
• B. sodium
• C. zinc
• D. tungsten

Answer 1

The correct option is B

sodium

• Arrangement of the metals on the basis of their reactivity towards other elements is termed as activity series. Elements at the top of this series are comparatively more reactive than elements below in the series.
• Among the given elements, Sodium $\left(\mathrm{Na}\right)$ is present at the top of the reactivity series and therefore, it is highly reactive in nature. Sodium $\left(\mathrm{Na}\right)$ reacts with cold Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ to form Sodium hydroxide or Caustic soda $\left(\mathrm{NaOH}\right)$ and Hydrogen molecule $\left({\mathrm{H}}_2\right)$.

$2\mathrm{Na}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

• Since Mercury $\left(\mathrm{Hg}\right)$, Zinc $\left(\mathrm{Zn}\right)$, and Tungsten $\left(\mathrm{W}\right)$ are present at the bottom of the reactivity series, these elements do not undergo reaction with cold water.

Hence, option (B) is correct. Sodium reacts with cold water.