alleryWhy are giant covalent crystals (like diamond) very hard?
AThey have ionic bonds in standard practice
BThey have hydrogen bonds
CThey have a 3D network of strong covalent bonds
DThey have metallic bonds
Answer & Solution
Correct answer: C. They have a 3D network of strong covalent bonds
1. Diamond's structure is a 3D lattice where every carbon is bonded to four others.
2. All bonds are strong C-C covalent bonds.
3. Breaking the crystal needs breaking many such bonds.
4. Hence diamond is very hard.
5. The same principle applies to silicon and silicon carbide.
_Source: Selina Concise Chemistry ICSE Class 10, Ch 2 'Chemical Bonding'_
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