If 20 joules of work is used to transfer 20 coulombs of charge through a 20 ohm resistor, the potential difference across the resistor is

The answer is 1 V.

This is because the equation for Potential difference is work done over the charge it has passed through between two points. So basically V = W/q.

So now as we know the formula for the potential difference we can simply calculate the potential drop across the resistor by plugging in the values.

From this we get V = 20/20 so the answer comes out to be 1 Volt. Or 1 V.