Combination of Resistors question from JEE Main 2023 (10 Apr, Shift 1)

Answer: (c)

1. By symmetry the top vertex and the centre are both midway in potential between a and b (each joined by $4\ \Omega$ to a and to b), so the vertical $4\ \Omega$ carries no current.
2. Paths: a–top–b $= 8\ \Omega$, a–centre–b $= 8\ \Omega$, direct $16\ \Omega$, all in parallel.
3. $\dfrac{1}{R} = \dfrac18 + \dfrac18 + \dfrac1{16} = \dfrac{5}{16} \Rightarrow R = 3.2\ \Omega$
4. So the answer is (c) $3.2\ \Omega$.