S. 10 (23C): Educational institution-Filing of return-total income of the assessee without giving effect to the provisions of s. 10(23C)(iiiad)] exceeded the maximum amount not chargeable to income-tax-Not required to file return of income either under section 139(1) or under section 139(4C)]-Return filed in response to section 148 cannot be treated as invalid]-Disallowance of claim was not justified. [S. 10(23C)(iiiad), 139(1) 139(4C), 148]