The Correct Answer is kPa dm6 mol^(-2). Explanation & Key Takeaways: • The ideal gas law considers the molecules of gas with perfectly elastic collisions as point particles. • Gas molecules do not have point masses, and there are several situations in which gases must be regarded as non-ideal. • Johannes D. van der Waals had proposed the modification to take the molecular size and molecular interaction forces into account. • It is normally referred to as the state equation of van der Waals: • [P + a(n/V)^(2)] (V/n - b) = RT • The a and b constants are called the constants of van der Waals. • They have positive values and the individual gas is characteristic. • If a gas acts ideally, both a and b are zero, and the ideal gas law: • PV=nRT approaches the van der Waals equations.