Question

give reasons diamond is use an abrasive

Answer 1

An abrasive is a substance that is used to grind, polish or clean a hard surface by rubbing the two against each other. The substance used as an abrasive is always the harder than the one being polished.  Carbon atoms in diamond forms a rigid, covalent three dimensional network where each sp3 hybridized carbon forms covalent bond with four adjacent carbon atoms, which makes diamond very hard . As diamond is the hardest of all natural substances and therefore the best candidate to be used as an abrasive. 

Answer 2

Diamond is used as an abrasive because of its hardness.