Provided that no penalty under this sub-section shall be imposed, unless the assessee affected has had a reasonable opportunity of showing cause against the imposition of such penalty.

Assessment of escaped or under-assessed tax If for any reason any tax payable under this Act has escaped assessment or has been under-assessed or assessed at a lower rate than the rate at which it is assessable, the assessing authority may, at any time within five years from the expiry of the year to which the tax relates, proceed to assess or reassess the tax, as the case may be, to the best of his judgment, after issuing a notice to the assessee concerned and after making such enquiry as he considers necessary:

Provided that the tax shall be charged at the rate at which it would have been charged if such tax had not escaped assessment or, as the case may be, had not been under-assessed or assessed at a rate lower than the rate at which it was assessable.