Debentures carry interest at:

Fixed-rate of interest

The correct answer is option 3- Fixed-rate of interest.

Debentures carry a fixed rate of interest, which is specified at the time of issue. This rate can vary from one issue to another (e.g., 5%, 8%, 11%, etc.), but the key point is that it is fixed and predetermined. The other options (10%, 5%, 15%) are just examples of possible rates, not universally applicable.