Correct Answer - Option 3 : 300 J/kg
Concept:
From the first law of thermodynamics
dQ = dU + dW
dQ = -400 J ( As the heat is rejected from the system)
dW = -1000 J ( as work is supplied to system)
Change in internal energy, dU = dQ – dW = -400 – (-1000) = 600 J
Change in specific internal energy = 600/2 = 300 J/kg (mass is 2 kg)