Interest payable on debentures is calculated at which value?

The correct answer is option 1- Nominal value.

When a company issues debentures, it is under an obligation to pay interest thereon at fixed percentage (half yearly) periodically until debentures are repaid. This percentage is usually as part of the name of debentures like 8% debentures, 10% debentures, etc., and interest payable is calculated at the nominal value of debentures.