Solid A is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it?

Hint:We are asked to find what type of solid is solid A. There are three properties of solid A given, understand each property. Recall a type of solid which satisfies or has these three properties. Compare this solid which has the three given properties with the given solid A.

Complete answer:
Given, a solid A which is a very hard electrical insulator in solid and also in molten state and it melts at extremely high temperature.There are three properties of solid A given which are very hard, electrical insulators and melts at extremely high temperature.By electrical insulator we mean, materials through which electric current do not flow easily that is, electrons do not flow easily through the material.

We know materials having covalent bonds do not conduct electricity due to lack of free electrons in the material.It is said that the solid A is very hard and is an electrical insulator which means the atoms in solid A are bound together by covalent bond. And as covalent bonds are strong, it has a higher melting point, therefore it satisfies the third property too.

Hence, solid A is a covalent solid.

Note:Here we have discussed covalent bond. There are four types of bonding, these are metallic bond, ionic bond, covalent bond, and hydrogen bond. The strongest bond is the covalent bond and the weakest bond is the hydrogen bond. Some examples of substances having covalent bonds are diamond, water and ammonia.