Which reaction below represents the first ionization of O? a. O (g) + e - → O - (g) b. O + (g) + e - → O (g) c. O (g) → O + (g) + e-d. O - (g) + e - → O2 - (g) e. O - (g) → O (g) + e-

option C = O (g) → O + (g) + e-

Explanation:

Definition:

" The ionization energy is the energy required to remove the electron from outer most shell"

First ionization energy:

"It is the amount of energy required to remove the very first electron from valance shell"

it is represented in following equation;

X (g) → X + (g) + e-

The physical state (g) must be written because ionization process occur in gaseous phase. The ionization energy always measured in KJ/mol. The ionization energies are always positive because electrons are attracted towards the nucleus and energy is always require to remove the electron and to overcome the hold of nucleus.

Periodic trend:

As we move down the group the ionization energies decreases with the increase of atomic number because atomic size increases and hold of nucleus or nucleus attraction on valance electron became weaker. that's way less energy is required to remove the electron.

As we move left to right in periodic table the ionization energy increase with increase of atomic number because atomic radius decreases and electrons are attracted towards the nucleus that's way more energy is required to remove the electron.

First ionization energy of oxygen:

O8 = 1s2 2s2 2p4 (1st ionization energy = I. E. = 1310 kJ/mol

The electron is remove from 2p subshell.