Deductions are allowed after arriving Gross Total Income ie. after aggregation and set-off. If GTI is zero no deduction would be available. Where as exempted item of income would not form part of Total Income. Exemption is given before aggregation and set-off.
this can be illustrated as below:
X is a co-operative society having business income Rs 5,00,000/- and house property loss Rs3,00,000/-. Its business income is eligible for deduction u/s 80P.
in this case GTI is 5,00,000 + (-) 3,00,000 = 2,00,000
Less; deduction u/s 80P = 2,00,000 ( though BI is 5 lakh deduction is limited to GTI available)
Taxable income = Nil
If in the above case no deduction u/s 80P is avilable but BI includes exempt income to the tune of Rs 4,00,000
then GTI is (5,00,000 - 4,00,000) + (-) 3,00,000 = (-) 2,00,000
Taxable income = Nil ( HP loss 2 lakh will be allowed to carry forward)