If the work done on a system is 500 J and 200 J of heat is lost, what is the gain in internal energy?

200 J

300 J

400 J

None of these

According to the first law of thermodynamics, ΔU = Q + W.

Here, heat lost (Q) = -200 J, work done on the system (W) = 500 J.
ΔU = (-200 J) + (500 J) = 300 J.