The value of y = c_p/c_v. at < 500°C for air & most common gases can be safely assumed to be

ANS:C - 1.4

The value of cv/​cp​​, also known as the specific heat ratio or adiabatic index, at temperatures below 500°C for air and most common gases can be safely assumed to be approximately 1.4. The specific heat ratio (cv/​cp​​) is the ratio of the specific heat at constant pressure (cp​) to the specific heat at constant volume (cv​). For ideal diatomic gases like oxygen (O2​) and nitrogen (N2​), as well as for air (which is a mixture of oxygen and nitrogen), the specific heat ratio is approximately 1.4 over a wide range of temperatures and pressures. This value of 1.4 is a commonly accepted approximation for many engineering calculations involving gases, especially at temperatures and pressures within the range encountered in typical engineering applications.