A wire having resistance 20 ohm is bent to make a closed square. What is the resistance across the diagonal of square?

5 Ω

Explanation:

When it is bent into a square, each side of the square will get 5 Ω resistance. As considered diagonally ,path of the wire between to diagonal points is the two sides of the square (that is half the length of the wire connected in parallel position). Which gives 10 ohm parallel to 10 ohm wire. So it finally read as 5 Ω wire