question_answer 67)

  Helium atom has 2 electrons in its valence shell but its valency is not 2. Explain.

Answer:

  Helium atom has only one shell (K shell) which can have maximum 2 electrons. Thus, its shell is already complete called duplet. It can neither lose electrons nor gain electrons. Hence, its valency is 'zero'. It is called noble gas or inert gas.