An element X has a mass number 4 and atomic number 2. Write the valency of this element?


  • Mass number = 4
  • Atomic number = 2

X is Helium.

It has 0 valency and it will not react with any other atom because it has its outer shell filled.

Valency of inert gas

  • Valency is a combining capacity of an element. As there are no free electrons in the valence shell and the elements are already in a stable state, the noble gases’ valency is zero.
  • The atoms of noble gases already have complete outer shells, so they do not lose, gain, or share electrons. This is why the noble gases are inert and do not take part in chemical reactions.
  • Nobel gas does not tend to lose electrons. Thus, the valency of inert gases is zero.

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