(a) where the proper officer is satisfied that an importer or exporter is unable to produce any document or furnish any information necessary for the assessment of duty on the imported goods or the export goods, as the case may be; or

(b) where the proper officer deems it necessary to subject any imported goods or export goods to any chemical or other test for the purpose of assessment of duty thereon; or

(c) where the importer or the exporter has produced all the necessary documents and furnished full information for the assessment of duty but the proper officer deems it necessary to make further enquiry for assessing the duty; the proper officer may direct that the duty leviable on such goods may, pending the production of such documents or furnishing of such information or completion of such test or enquiry, be assessed pro- visionally if the importer or the exporter, as the case may be, furnishes such security as the proper officer deems fit for the pay- ment of the deficiency, if any, between the duty finally assessed and the duty provisionally assessed.

(a) in the case of goods cleared for home consumption or ex- portation, the amount paid shall be adjusted against the duty finally assessed and if the amount so paid falls short of, or is in excess of, 1[ in duty finally assessed] the importer or the exporter of the goods shall pay the deficiency or be entitled to a refund, as the case may be;

(b) in the case of warehoused goods, the proper officer may, where the duty finally assessed is in excess of the duty provisionally assessed, require the importer to execute a bond, binding himself in a sum equal to twice the amount of the excess duty.