This video discusses the applicability of ideal gas equation to estimate the density of an ideal gas. Ideal gas law can be used when gas is at low pressure and high temperature. A criterion involving specific molar volume is given to justify the use of ideal gas law for different gases. Later part of the video discusses how to use ideal gas law when you don't remember the value of Gas Constant in the given units. The method described over here reduces computational efforts. Numerical examples have been taken to explain this.