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

It is given that the element reacts with oxygen to give a high melting point .

• Hence, the element must be very reactive and must form an ionic bond .
• Ionic bonds are are formed between electropositive metals and electronegative non-metals
• Carbon and Silicon are neither electropositive nor electronegative. They form covalent bonds . 

• So, the element can either be Calcium or Fe 

It's also given that the compound is soluble in water.

• The metal must be an alkali metal.
• From the given options, only Calcium is an alkali metal.

Therefore, the element is most likely to be Calcium (Ca) .

So, the correct answer is (a)