Question

An element reacts with oxygen to give a compound with a high melting point. This compound is also water soluble. The element is likely to be:

• A. Calcium
• B. Carbon
• C. Silicon
• D. Iron

Answer 1

The correct option is A Calcium

Calcium combines with oxygen to form calcium oxide ($\text{CaO}$) which dissolves in water to form calcium hydroxide. The reaction involved is as follows:

$2\text{Ca(s)}+{\text{O}}_2\text{(g)}\to 2\text{CaO(s)}$
$\text{CaO(s)}+{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(l)}$

Calcium oxide has high melting point. When carbon reacts with oxygen, carbon dioxide gas is a formed and gases do not possess melting point.

Silicon and iron react with oxygen to form their respective oxides ${\text{(SiO}}_2\text{\&}\text{FeO)}$ , but they are insoluble in water.