Step 1: Meaning of collateral security.
When debentures are issued as collateral, they are not for raising capital but as additional security against a bank loan.
Step 2: Accounting treatment.
To show liability correctly, Debenture Suspense A/c is debited and Debenture A/c is credited.
Journal entry:
\[
\text{Debenture Suspense A/c Dr. \quad To Debentures A/c}
\]
Step 3: Conclude.
Thus, Debenture Suspense A/c is debited.
Final Answer:
\[
\boxed{\text{Debenture Suspense A/c}}
\]