What characteristic of helium distinguishes helium from the other noble gases?

The characteristic that helium has that distinguishes it from the noble gases would be that it only has 2 valence electrons while noble gases has a completely filled orbitals giving it 8 valence electrons and a stable electron configuration. The valence electrons is the number of electrons that is present in an atom that can take part in the formation of bonds. These electrons can be found on the outermost shell of an atom. Helium is an exception to the octet rule, its atom has only two available electrons in its outermost shell since it only has one eletron shell that is the only the s orbital which can hold two electrons only. 

Adozen is 12, and your needing to calculate the weight of one medium egg, so i would do 21/12=1.75 per egg, and check your answer by doing 1.75 * 12= 21 : ) : ): ): ): ) i hoped i

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.