The first ionisation energies of the elements of group 14 follow the order.

Options

A. `C gt Si gt Ge gt Pb gt Sn`
B. `C gt Si gt Ge st Sn gt Pb`
C. `C lt Si gt Ge gt Sn gt Pb`
D. `Si gt C gt Ge gt Sn gt Pb`

Answer

To determine the order of first ionization energies of the elements in Group 14 (carbon, silicon, germanium, tin, and lead), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements**: The elements in Group 14 are carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).

2. **Understand Ionization Energy**: Ionization energy is the energy required to remove the outermost electron from an atom. Generally, ionization energy increases as you move up a group in the periodic table due to decreasing atomic size and increased nuclear charge.

3. **Consider Atomic Size**: As we move down the group from carbon to lead, the atomic size increases. This is because additional electron shells are added, which increases the distance of the outermost electron from the nucleus.

4. **Effect of Atomic Size on Ionization Energy**: With an increase in atomic size, the outermost electron experiences less attraction from the nucleus due to the increased distance. Therefore, the ionization energy generally decreases as we move down the group.

5. **Identify the Exception**: While the trend indicates a decrease in ionization energy from carbon to lead, there is an exception with lead (Pb) having a higher ionization energy than tin (Sn). This is due to the inert-pair effect, where the d and f orbitals do not shield the outermost electron effectively, leading to a stronger attraction from the nucleus for lead.

6. **Order of Ionization Energies**: Based on the above analysis, the order of first ionization energies from highest to lowest is:
- Carbon (C) > Silicon (Si) > Germanium (Ge) > Lead (Pb) > Tin (Sn)

### Final Order:
The correct order of first ionization energies in Group 14 is:
**C > Si > Ge > Pb > Sn**