8. Assessment of an assessee

(1) If the assessing authority is satisfied that the return submitted by an assessee is correct and complete, it may accept the return. If the return appears to it to be incorrect or incomplete  it shall, after giving the assessee a reasonable opportunity of proving the correctness or completeness of the return submitted by him and making such enquiry as  it deemed necessary, assess to the best of its judgment, the amount of tax due from the assess. 

Rule 12(2)

(2) The amount of tax due from any assessee shall be assessed separately for each yearwithin a period of four years from the expiry of the year to which the assessment relates. 

(3) If any assessee has failed to get himself registered or having been registered, has failed to submit any return, the assessing authority shall,  after giving the assessee a reasonable opportunity of making representation and after making such inquiry as he deems necessary pass an order assessing the amount of tax due, to the best of in judgment.

Rule 12(2) & 16

(4) The amount of tax so assessed shall be paid within fifteen days of receipt of the notice of demand from the  assessing authority.

Rule 18

(5) In making an assessment under sub-section (1), the assessing authority if it is satisfied that the escaped assessment  was due to wilful nondisclosure of information or attempt  to evade the tax by the assessee, the assessing authority  may also direct to pay in addition to the tax assessed a penalty which shall not be less than one and half times the tax so assessed but which shall not exceed three times the tax so assessed:

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.