If exact 40 lakhs then no need becoz provision says exceeds so if exact 40 lakhs then no need if exceeds 40 lakhs even rupee then registration required
Yes, you can opt for composition scheme..if have only intra state sale ( inter State Purchase allowed) and T/O less than 1.5 crore (75 lakh for North-eastern State)
If you are only Purchasing and selling scrap as like only Trading..than you can opt as trader @ 1% Composition rate.