Question

Mohan can see his face clearly in a new stainless steel plate but not in the old one

Answer 1

because stainless steel acts as a mirror
on a new one there are no marks and scratch so we are able to see clearly in the new one not in old one

Answer 2

Because stainless steel plate which is new is recently polished so it reflects nicely and acts as mirror but in the case of old plate, all the polishing is removed, so we cannot se our face in that old plate clearly.