(5)If any person--(a)fails to make the return required under sub-section (1) of section 13 and has not made a return or a revised return under section 14, or(b)fails to comply with all the terms of a notice issued under sub-section (2) or subsection (4), the Assessing Officer, after taking into account all relevant material which he has gathered, shall, after giving such person an opportunity of being heard, estimate the value of taxable gifts to the best of his judgment and determine the sum payable by such person on the basis of such assessment:Provided that such opportunity shall be given by the Assessing Officer by serving a notice calling upon the person to show cause, on a date and time to be specified in the notice, why the assessment should not be completed to the best of his judgment:Provided further that it shall not be necessary to give such opportunity in a case where a notice under sub-section (4) has been issued prior to the making of the assessment under this sub-section.
