" What is compressibility factor? "

(a) What is meant by compressibility factor of a gas ? Is it always equal to or greater than 1 for all gases? (b) 1 mole of SO_(2) occupies a volume of 320 mL at 27^(@)C and 4xx10^(6)Pa pressure. Calculate the compressibility factor of the gas. (2+3)

For an ideal gas, compressibility factor is

What is meant by the term compressibility factor ?