Answer: Option (a) is the correct answer.
Explanation:
It is known that chemical properties of an atom depends on the number of electrons in its outermost shell, that is, valence shell.
For example, Na has 1 electrons in its valence shell and K also has 1 valence electron as both Na and K belongs to the same group.
Therefore, vertical columns in the periodic table represent groups and horizontal lines represent period.
Thus, we can conclude that elements listed in vertical columns of the periodic table have similar chemical properties.
