Question

In a group, the ionisation energy decreases from top to bottom because of

• A. increase in atomic size
• B. decrease in chemical reactivity
• C. decrease in electronegativity
• D. increase in density

Answer 1

The correct option is A

increase in atomic size

The enthalpy change associated with the removal of the first electron from an isolated gaseous atom in its ground state is called first ionization enthalpy.

As one moves down the group,

1. The atomic size gradually grows larger.
2. As a result, the force of attraction between the nucleus and the electron decreases.
3. As a result, only a small amount of energy is required to remove an electron from the outermost shell, and

As a result, the ionization energy decreases down the group.

Hence, option(a) is correct.