Determination of unpaid tax: notice to show cause, interest and penalty consequences for nonpayment and erroneous credits. Determination of unpaid, short paid, erroneously refunded tax or wrongly availed input tax credit is initiated by the proper officer by serving a notice to show cause requiring payment of specified tax with interest and penalty, subject to limitation. A statement for additional periods may be served as notice if based on the same grounds. Voluntary payment of tax and interest before notice bars further notice for amounts paid, though insufficiency permits further notice. Payment within thirty days of show cause notice removes penalty. The proper officer, after considering representations, determines tax, interest and penalty and issues an order within the limitation period.