Which is the hardest in the following?

Correct answer: (a) Diamond

Explanation

Diamond is the hardest natural substance, 10 on the Mohs scale. Each carbon atom is bonded strongly to four others in a rigid three-dimensional network.

That is why diamond is used to cut glass and in drill bits. Quartz is 7 on the Mohs scale, glass about 5.5 and platinum about 4.