PLEASE HELP!(physics question class 10)? answer is 2 ohm but how to solve it?

This type of circuit is called a Wheatstone bridge.
Since all 4 outside resistors here are the same, the exact same voltage is on each end of the 10 ohm resistance. Because it is identical, NO current flows through the 10 ohm. You could just snip it out of circuit, nothing would change.
So what you have then is 2 resistors each side in series (left side and right side) = 4 0hms each side.
The 2 sides are in parallel, so the equivalent value is 2 ohms overall.

From symmetry, there is no current in the 10 ohm resister. It might as well not be there. So the top part is just 4 ohm, and the bottom is 4 ohms. Those are in parallel, so the combined resistance is 2 ohms.