Question

The hardest compound of boron is :
A. boron carbide
B. boron sulphide
C. boron fluoride
D. boron nitride

Answer 1

Hint: We know that the molecular formula of boron carbide is ${B_4}C$, molecular formula of boron sulphide is ${B_2}{S_3}$, molecular formula of boron fluoride is $B{F_3}$ and the molecular formula of boron nitride is $BN$.The force of attraction between the atoms of the compound and the structure of the compound defines the hardness of the compound.

Complete answer:
We know that the hexagonal structure of boron nitride is very similar to that of graphite. The bonds between the boron and nitrogen atoms are very strong. Carbon carbide is also one of the hardest substances known to us but diamond and boron nitride are much harder than boron carbide. Boron sulphide and boron fluoride are not harder than boron carbide and boron nitride. Boron carbides are so hard that they can even scratch diamond which is the hardest substance on earth. Boron nitride is extremely hard. Boron nitride has a very high melting point and it is very inert in nature. Boron nitride is used as abrasive and wear resistant coating.
Boron nitride is produced when boron reacts with nitrogen in air. The chemical equation can be written as $2B + {N_2} \to BN$.
So from the above explanation and discussion it is clear to us that

The correct answer of the given question is option: D.

Note: Always remember that boron nitride is the hardest compound of boron. Boron carbide is also one of the hardest compounds known to us but is not harder than diamond and boron nitride. Boron nitride is produced when boron reacts with nitrogen in air $2B + {N_2} \to BN$.