Non-convertible debentures are debt instruments that cannot be converted into equity shares. Since they represent a liability that the company is obligated to repay with interest, they are classified as loan capital or long-term debt rather than equity or owner's capital.

When a company issues debentures as collateral security, it means these debentures are given to the lender as an additional or secondary guarantee for a loan. If the company defaults on the primary loan, the lender can exercise their rights over these debentures to recover the outstanding debt.

A loss on the issue of debentures is considered a fictitious asset. It is not a tangible asset that can be sold, but rather a deferred expenditure that is written off over the life of the debentures against the company's profits.

A zero-coupon bond is a security that does not make periodic interest payments. Instead, it is issued at a significant discount to its par value. The investor's return is the difference between the purchase price and the face value received at maturity. Because there are no interim cash flows, these bonds are highly sensitive to changes in market interest rates and are often used for long-term financial planning.

Collateral debentures are issued by a company to a lender as secondary or additional security for a loan. If the company defaults on the primary loan, the lender can exercise their rights over these debentures to recover the outstanding debt amount.

Corporate bonds are debt securities issued by companies to raise capital for operations or expansion. Unlike government securities, these bonds are subject to default risk, which is the possibility that the issuing corporation may fail to make interest or principal payments. Investors typically demand a higher yield on these bonds compared to risk-free government bonds to compensate for this credit risk.

A premium on the issue of debentures occurs when the company issues debt at a price higher than its face value. Since this is a gain related to the capital structure of the company rather than normal trading operations, it is classified as a capital profit.

Zero-coupon bonds (a-2) are issued at a discount without periodic interest. Income bonds (b-3) pay interest only when the company earns sufficient profit, reducing financial distress. Floating rate bonds (c-1) feature interest rates that adjust based on a benchmark index or mark-up, reflecting market conditions.

The provided answer suggests debentures cannot be registered; however, in standard corporate practice, most debentures are indeed issued as registered instruments where the holder's name is recorded in the company's register. This allows the company to track ownership for interest payments. The claim that they cannot be registered is factually inconsistent with common financial regulations and standard accounting practices.

Redeemable debentures are debt instruments. Even if they have matured and are awaiting payment, they retain their character as secured debt until fully discharged. Therefore, they are typically classified under secured loans in the balance sheet until the actual cash outflow occurs. Note: In some modern accounting frameworks, these might be reclassified as current liabilities if payment is due within the next operating cycle, but the provided answer identifies them as secured loans.