Short answer

Market orders are blocked for trade-to-trade and debt category instruments due to their illiquid nature. A lack of liquidity means that the bid and ask spread in the instrument is very high and can have an immediate adverse effect on your profit and loss (P&L). The bid/ask price could be at a price far from the last traded price or the theoretical price of the contracts. However, you can use a limit order as a market order to execute this transaction safely.

Market orders for all non-EQ category instruments are blocked. To learn more about different categories, see What do the different groups on NSE and BSE mean?