Recall that the resting potential is established by the diffusion of K+ ions out of the cell through non-voltage gated channels (“leak channels”) in the membrane. The Na+/K+ ATPase maintains a high intracellular concentration of K+ relative to the extracellular environment by pumping 2 K+ ions into the cell (and 3 Na+ ions out of the cell).
If the membrane were to become impermeable to K+ ions (i.e. the membrane would not allow the passive efflux of K+ ions out of the cell through these “leak channels”) but the Na+/K+ ATPase continued as normal, then K+ ions would continue to enter the cell via the Na+/K+ ATPase but no K+ ions would leave. Thus, the K+ concentration inside the cell would be greater than if the membrane were permeable to K+ ions (and accordingly, the resting potential would become more positive, answer choice A).
Does this help?