Question

An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in the air. It reacts vigorously with water. Identify the element from the following

• A. $\mathrm{Mg}$
• B. $\mathrm{Na}$
• C. $\mathrm{P}$
• D. $\mathrm{Ca}$

Answer 1

The correct option is B

$\mathrm{Na}$

Explanation for correct option

(B)$\mathrm{Na}$

• Sodium is so soft that it can be cut with a knife.
• It reacts vigorously with oxygen when kept open in the air and hence, we keep it immersed in kerosene oil.
• It also reacts vigorously with water and air.

Explanation for incorrect option

An element A is a sodium. Hence, options (A),(C), and (D) are incorrect.

Hence, option (B) is correct. An element “sodium” is soft and can be cut with a knife.