Depends on the contract you are trading. If you are trading Nifty, makes no difference. But yes, if you are trading stock futures, you can get hit in terms of the impact cost.
Not really to bother about, if you are trading Nifty Index Futures/Options.
Use limit order if you want to eliminate slippage issue.
In case of market orders, you should have a look at the Snap quote or Market Depth information to see what is the next 5 best available bids/asks.
If within the next 5 bids/asks you are comfortable with getting 50 lots sold/bought (with less slippage), you can go ahead and issue a market order.
Doesn’t the impact cost affect only in case of market orders?