Question

An element with variable (more than one) valency stored under water is:

• A. silicon
• B. iron
• C. phosphorus
• D. gold

Answer 1

Answer: (C)

phosphorus

Phosphorous can accept either 3 electrons or donate 5 electrons anyways it depends on the neighborhood element. Here it has variable valency. The allotropic form of phosphorus (white phosphorus) is less stable and therefore highly reactive because of angular strain in $P_4$ molecule where the angles are only ${60}^o$. It readily catches fire in air to give dense white fumes of $P_4{O}_{10}$. Therefore, it is kept in water to avoid oxidation by the oxygen present in the air. It is kept in water because it is insoluble in water.