Chapter 6 - Gases - Example 6-8 - Using the Ideal Gas Equation to Calculate a Gas Density - Page 209: Practice Example A

$d=0.162 \,g/L$ As the density of helium is much lesser than the density of air, we can say that helium is lighter than air.

$d=\frac{MP}{RT}=\frac{(4.0026\,g/mol)(0.987\,atm)}{(0.08206\,L\,atm\,mol^{-1}K^{-1})(298\,K)}$ $=0.162 \,g/L$ As the density of helium is much lesser than the density of air, we can say that helium is lighter than air.