Step 1: Read the clue:
The question says a charge is created on the assets of the company. The charge is for payment if the company fails to pay.
So the debenture holders have a claim on specific assets. This is the feature we must name.
Step 2: Recall the meaning:
A debenture is secured when the repayment of the money and the interest is backed by a charge on the assets of the company.
If the company defaults, the holders can sell the charged assets to recover their money. Such debentures are called secured debentures.
Step 3: Why the other options are wrong:
Option (A) Unsecured: these have no charge on any asset. Holders rank like ordinary creditors, which is the opposite of the clue. Wrong.
Option (C) Convertible: these can be changed into equity shares after a stated time. This is about conversion, not about a charge on assets. Wrong.
Option (D) Registered: the name of the holder is entered in the register of the company. This is about who owns the debenture, not about security. Wrong.
Final Answer:
The blank is filled by Secured, which is option (B).