Question

Which of the following reacts with cold water vigorously?

• A. Carbon
• B. Sodium
• C. Magnesium
• D. Sulphur

Answer 1

The correct option is B

Sodium

Explanation of the correct option:

B. Sodium

• The alkali metal $\mathrm{Na}$ is the most reactive metal and they react vigorously with cold water.
• They are highly reducing in nature.
• It results in the displacement of hydrogen.

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

Explanation of incorrect options:

(A) Carbon

• $\mathrm{C}$ does not react with water under normal conditions, only at high temperatures, they can react with water.

(C) Magnesium

• In general $\mathrm{Mg}$ is a slow reactive reacting element and when $\mathrm{Mg}$ reacts with hot water, magnesium hydroxide $\mathrm{Mg}{\left(\mathrm{OH}\right)}_2$ and hydrogen are formed.
• The chemical reaction can be depicted as:

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{MgOH}}_2\left(\mathrm{s}\right)$

(D) Sulfur

• When sulfur $\left(\mathrm{S}\right)$ react with oxygen $\left(\mathrm{O}\right)$, it forms sulfur dioxide $\left({\mathrm{SO}}_2\right)$ .
• The chemical reaction can be depicted as:
• $\mathrm{S}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{SO}}_2\left(\mathrm{g}\right)$

Hence, the correct option is B i.e. Sodium.