S. 143(1) : Assessment-Intimation-Failure to file Form No 10B-Adjustment is justified-Disallowance of expenditure-Revenue is directed to intimate the exact reason for disallowing the claim of the assessee while processing the return-The assessee may file an application under S. 154 to rectify the mistake in the intimation, as deemed proper-Assessee is also free to avail the remedy under s. 119 if it so desires. [S. 10(23C), 11, 119, 154, 250(5)]