Ideal gas law:

The constant R, called the gas constant, has the value     when all quantities in the ideal gas law are expressed in SI units—P in Pa, V in m3, n in mol, and T in K. Alternatively if we express V in L, P in atm, n in mol, and T in K,

The ideal gas law is valid only for ideal gases. All gases can be liquefied at sufficiently high pressure and low temperature and gases become nonideal as they approach liquefaction. However, almost all gases behave nearly ideally at temperatures significantly above their boiling points and at pressures of a few atmospheres or less.