QJEEM18Ph0821: JEE Main 2018 Physics - Class 12 JEEM18Ph0821 Solution: In the given circuit all resistances are of value R o h m each. …

Let us assume potential at point M is X volts. Now you can see a plain wire is directly connected between point N and point M so point N will also have same potential as point M.

Similarly, a plain wire is directly connected between point N and point O so point O will also have same potential as point N.

Also, a plain wire is directly connected between point O and point P so point P will also have same potential as point O.

Now you can see point P and point M both have same potential X, so no current will flow through that path so you can remove that resistor. Similarly, as point O and point M both have same potential X, so no current will flow through that path also so you can remove that resistor too.

So new circuit becomes
$$\therefore$$ R_AB = R + R = 2R