Why do elements in the same group on the periodic table tend to have similar physical and chemical properties? A
They have the same atomic mass.

B
They have the same number of protons.

C
They have the same number of valence electrons.

The answer is C

Explanation:

In chemistry, a group is a vertical column in the periodic table of the chemical elements. Each element within a group has similar physical or chemical properties because of its atom's outermost electron shell (most chemical properties are dominated by the orbital location of the outermost electron).

So the answer will most likely be C

i would say