(b)after the beginning of commercial production, to expenditure incurred by the assessee, whether before or after such commercial production, in respect of drilling or exploration activities or service or in respect of physical assets used in that connection, except assets on which allowance for depreciation is admissible under section 32 [*] [ The word " and" omitted by Act 16 of 1981, Section 8 (w.e.f. 1.4.1981).]: