Question

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

(a) calcium

(b)carbon

(c)silicon

(d)iron

Answer 1

Pure calcium oxide or lime, is an amorphous white solid, having a high melting point (2273K). When lime is added to water, a hissing sound is produced and a large amount of heat is generated.

Cao + H₂O------> Ca(OH)₂ + Heat
Therefore, the correct answer is (a).