For the reversible isobaric change of an ideal gas undergoing a process in a pistoncylinder assembly, the change in entropy will be

(a) \((\Delta S)_{P}=C_{P} \ln \frac{T_{2}}{T_{1}}\)

(b) \((\Delta S)_{P}=C_{P} \ln \frac{V_{2}}{V_{1}}\)

(c) \((\Delta S)_{P}=C_{P} \ln \frac{T_{1}}{T_{2}}\)

(d) None of these.