Excise duty exemption on potassium chlorate caps the payable duty to a prescribed ad valorem rate under statutory rule. Under sub rule (1) of rule 8 of the Central Excise Rules, 1944, potassium chlorate falling under sub heading 2829.10 of the Central Excise Tariff Act, 1985 is exempted from that portion of excise duty which exceeds the amount calculated at a prescribed ad valorem rate, thereby capping the effective duty payable on that tariff entry.