Q.Find the odd one.

A mortgage debenture is a secured debenture backed by a charge/mortgage on the company's assets.

A mortgage (secured) debenture is one whose principal and interest are secured by creating a charge over the assets of the company — either a fixed charge on specific assets or a floating charge on all assets. If the company fails to pay interest or repay the principal, the debenture holders (through the trustees) can enforce the charge and sell the mortgaged assets to recover their money. This security makes mortgage debentures safer than 'naked' or unsecured debentures, which carry no such cha …

The correct option is partly or fully. Convertible debentures may be either partly convertible or fully convertible.

A convertible debenture gives the holder the right to convert the debenture into equity shares of the company after a stated period, on agreed terms. There are two forms of this. In a fully convertible debenture, the entire face value is converted into equity shares. In a partly convertible debenture, only a portion is converted into shares while the remaining portion continues as a normal debenture and is repaid on maturity.

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The odd one out is Irredeemable debentures. Secured and convertible debentures are valid types a company may issue, but irredeemable (perpetual) debentures cannot be issued under the Companies Act, 2013.

• Secured debentures are backed by a charge on the company's assets and can be issued.
• Convertible debentures can be converted into equity shares after a fixed period and can be issued. …