A wire of resistance 18 Ω is bent in the form of an equilateral triangle. The effective resistance between any two corners of the triangle is :

4 Ω

The correct answer is Option (4) → 4 Ω

When wire is bent into an equitorial angle, and the total resistance of the wire is 18 Ω.

$R_{side}=\frac{18 Ω}{3}=6Ω$

$R_{A→B→C}=6+6=12Ω$

$∴\frac{1}{R_{AB}}=\frac{1}{12}+\frac{1}{6}=\frac{3}{12}$

$\frac{1}{R_{AB}}=4Ω$