In the figure given, the value of X resistance when the potential differences between B and D is zero, is
4 ohm
6 ohm
8 ohm
9 ohm
Potential difference between B and D is zero, it means Wheatstone bridge is in balanced condition.
So PQ=RS ⇒ 213+ 8X8+X=186 ⇒ X=8 Ω