Answer
Even though Helium and the Group 2A metals have $ns^{2}$ outer electron configurations, Helium has a closed shell noble gas configuration and the Group 2A metals do not. The electrons in He are much closer to and more strongly attracted by the nucleus. Hence, the electrons in He are not easily removed. Helium is inert.
Work Step by Step
Even though Helium and the Group 2A metals have $ns^{2}$ outer electron configurations, Helium has a closed shell noble gas configuration and the Group 2A metals do not. The electrons in He are much closer to and more strongly attracted by the nucleus. Hence, the electrons in He are not easily removed. Helium is inert.