Which one of the following does not increase while moving down the group of the periodic table?

The correct option is C

Valence electrons

Explanation for correct option
(C) Valence electrons

• From left to right in the periodic table, the number of valence electrons increases.
• The number of valence electrons in a group remains constant from top to bottom.

Explanation for incorrect options

(A) Atomic radius

• Atomic radii increase down the group.

(B) Metallic character

• Metallic character increases down the group.

(D) Number of shells in an element

• Moving down a group in the periodic table, the number of shells increases which in turn increases.

Hence, the correct option is (C) Valence electrons.