Answer: Option (b) is the correct answer.
Explanation:
Valence electrons is the number of electrons present in the outermost shell of an atom.
So, when we move across a period from left to right then there will be increase in number of valence electrons.
For example, valence electrons in carbon is 4, nitrogen has 5 valence electrons, oxygen has 6 valence electrons.
Thus, we can conclude that number of valence electrons increases for elements change across a period.
