Step 1: Calculate the effective price per debenture:
Issue price = \rupee 100 - \rupee 4 = \rupee 96.
Step 2: Calculate the number of debentures:
Number of debentures = Total consideration ÷ Issue price
\[
\text{Number of debentures} = \rupee 24,00,000 ÷ \rupee 96 = 25,000.
\]
Conclusion:
The total number of debentures issued to the vendor is \( 25,000 \).