Hint: Helium is an element which has an atomic number of two and it can be found on the upper right side of the periodic table. It is considered to be the most significant member of the noble gas family. Helium has been classified as an inert gas because the outermost electron orbital of Helium contains two electrons.
Complete answer: • Valence electrons are generally referred to those electrons which are available in the outermost orbit of an atom. Using the concept of Bohr-bury theory, we can clearly say that the outermost shell can occupy a maximum of eight electrons. Also a little amount of chemical activity is observed when this (outermost) shell is completely filled. In other words we can see that its combining capacity has reduced to zero. • The outermost shell of the noble gases is completely filled and that is why they are the least reactive. An element’s reactivity depends upon its ability to attain the configuration of noble gas. ‘f’ is the outermost shell and if it has eight electrons then the element is known to have a complete octet. By receiving, sharing and giving the electrons the atoms complete their outermost orbital to achieve an octet target. • Helium has two electrons in its outermost shell that implies it has two valence electrons.
Note: Valency is quite different from the oxidation number as it is SIGN less which means it has no signs. On the other hand, the oxidation number is a hypothetical charge of an atom in a molecule which is a measure of its apparent capacity to lose or gain electrons within that species.