The question goes like this : If internal energy is not a state function, the first law of thermodynamics would be violated. Why ?
I answer the question in this way, if internal energy, U is not a state function, to reach a final state from an initial state, U would not be path independent. delta U = q + w. Therefore, there can be many pathways to reach from an initial state to another final state. i.e. delta U = q1 + w1, delta U = q2 + w2 but q1 + w1 is not = q2 + w2. For the same delta U, but q1 + w1 is not equal to q2 + w2, this implies that some energy must have been created or destroyed in the process and thus violating the first law of thermodynamics.
Is my answer correct and reasonable enough ?