In this case, your (collateral margin + free cash) = 1.6 lacs, so you will not be able to take an overnight F&O position of 2 lacs.
Allow me to change the values as below to explain:
Available collateral margin = Rs. 1.5lacs
(btw, collateral margin is what you receive when you pledge shares after an applicable haircut).
Available free cash = Rs. 50k.
Since (collateral margin + free cash) = 2 lacs, you can take an overnight F&O position of 2 lacs. At the end of the day, 1 lac is taken from the collateral margin and the other 1 lac is taken from free cash. But since you have only 50k free cash, 1.5 lacs is taken from collateral margin and only 50k is taken from free cash. Now for the 50k shortfall in free cash, you’ll be charged an interest of 0.05% per day.
Divide your F&O margin amount by 2 and ensure one half of this is available in free cash to avoid violating the 50% cash margin rule.
Also, read this post for some additional info.