If assessee is individual/HUF and there is Capital gain/loss, then ITR 2 is sufficient. This will be when you do trading on delivery basis and it is not your business.
If assessee is individual/HUF and has income from intraday trading (i.e. without delivery) or has traded in Futures and Options, then ITR 3 will be applicable.
If individual/HUF assessee does delivery based trading, and/or FnO and /or intraday trading then itr 3 will be applicable.