Casual income is taxable at a flat rate of 30%. No deduction under Chapter VI A or basic exemption limit is available for such income. However he can claim tax rebate upto Rs.12,500/- u/s 87A if his total income does not exceed Rs.5 Lacs.
Interest on housing loan can be claimed as follows- u/s 24(b) if Self occupied property- Max claim upto Rs.2 lacs. u/s 24(b) if let out- To the extent interest paid. The above do not come under Chapter VI A deductions.
But you cannot claim the HP loss against your casual income.