Fugacity and pressure are numerically equal, when the gas is

Answer: Option D

We know the concept of fugacity is originated from the equation $$d{\mu }_i=pdv-sdT$$    for an pure gas.
Under constant temperature and assuming an ideal gas we can write this as $$d\mu =RTdlnP$$    and for an real gas the same equation is assumed keeping all the non-ideality in the term fugacity and written as $$d\mu =RTdlnf$$
So, we can say for an ideal gas $$f=p.$$