Elements of the same subgroup have the same number of electrons on the outer layer. Am i right?

yes

Explanation:

because they have similar chemical properties

i believe it is c.) 1575 j.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.