DEAR MR SACHIN
The reply by Mr.Ramkumar contains everything. For a business all expenses incurred for running the business is allowable expenses. Anything which is in violation of the law or in the nature of personal expenses it is not allowed.
Also the INCOME TAX is not allowed as an expense since the same is tax on your net income.
For more details on allowable expenditure you may refer the DIRECT TAX LAWS
Regards
VENUGOPAL