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Diamond is very hard because

Asked in CBSE AIPMT 1993 · Bonding in solids

Answer: (2) it has large cohesive energy

Step-by-step solution

Idea: hardness measures how much energy it takes to break bonds and move atoms past one another.

In diamond every carbon atom is covalently bonded to four neighbours in a rigid three-dimensional network.

Breaking that network apart requires an unusually large energy per atom, which is what cohesive energy measures.

The large cohesive energy is therefore the direct reason for the hardness; the high melting point and covalent character are consequences of the same bonding.

Why the other options are wrong

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