Question

Question 25
An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following:
(a) $\text{Mg}$
(b) $\text{Na}$
(c) $\text{P}$
(d) $\text{Ca}$

Answer 1

Option (b) is correct.

Sodium is a soft, silver-white, highly reactive metal. It can be readily cut with a knife.

It reacts exothermically with water or moisture in the air, producing caustic soda (sodium hydroxide) and flammable hydrogen gas. It also reacts vigorously with oxygen in the air and produces sodium oxide.

Phosphorous, P, is a nonmetal. Ca and Mg are comparatively harder metals and do not react vigorously with cold water.