In which segment can I use the margin that was received after pledging mutual fund units?

While pledging iteslf you can choose the segment you want to get the collateral. Based on that collateral Margin will be available in the respective segment.

Below are the segments avialble for pledging mutual fund units

1. Equity (Cash) Segment
2. Equity Derivatives (F&O)
3. Currency Derivatives
4. Commodity