In the case of __________ the difference between the nominal value and the issue price is treated as the amount of interest related to the duration of the debentures.

Zero Coupon Debentures (or Deep Discount Bonds) do not carry a explicit periodic interest rate. Instead, they are issued at a significant discount relative to their face (nominal) value, and the total difference between the issue price and nominal value paid at redemption represents the interest earned over the duration.