Hydrogen gas caught fire quickly in the Hindenberg accident. In comparison, neon gas and helium gas are nonreactive. This is why helium is safe for aircraft and neon is safe for electrical signs. Which statement best explains why helium and neon have similar chemical properties?

Helium and Neon have similar chemical properties because both of them completely fill the outer shell of their atoms' electrons, so there is nothing to share with other atoms, neither with the same element nor with any other element.

Explanation:  

Helium and Neon are both  noble gases . As elements react, their atoms, by losing, acquiring, or sharing electrons, complete their outer shells. Noble gas atoms already have full outer shells, so there is no tendency for them to lose, gain, or share electrons. There are incomplete outer shells of atoms of group 1 and 7 elements (so they are reactive)

Chemical properties of HELIUM and NEON -:

Hence, helium and neon have similar chemical properties as they are the most stable due to having the maximum number of valence electrons their outer shell can hold.