For a stable phase at constant pressure and temperature, the fugacity of each component in a binary system __________ as its mole fraction increases.

Answer: Option B

We know for an ideal binary solution by Lewis-Randall rule fugacity of a component is directly proportional to mole fraction of that component. So basically on increasing the mole fraction the fugacity of the component is increasing but this equation is valid only for an ideal solution but, we can extend this behavior for real solution also under some conditions.