Circle the element with the LOWER IONIZATION ENERGY. 11. B or C
12. Ga or B
13. K or Ca
14.P or S
15. Co or Cr

Answers with detail given below.

Explanation:

Ionization trend along period:

As we move from left to right across the periodic table the number of valance electrons in an atom increase. The atomic size tend to decrease in same period of periodic table because the electrons are added with in the same shell. When the electron are added, at the same time protons are also added in the nucleus. The positive charge is going to increase and this charge is greater in effect than the charge of electrons. This effect lead to the greater nuclear attraction. As a result of this greater nuclear attraction atomic radius decreases and ionization energy increases.

Ionization trend along group:

As we move down the group atomic radii increased with increase of atomic number. The addition of electron in next level cause the atomic radii to increased. The hold of nucleus on valance shell become weaker because of shielding of electrons thus size of atom increased.

As the size of atom increases the ionization energy from top to bottom also  decreases.

Elements with lower ionization energy:

11) B

12) Ga

13) K

14) P

15) Cr