Question

Which of these is expected to have the highest ionization energy?

Atomic numbers of V, W, X, and Y are 10, 20, 30, and 40 respectively.

• A. ‘V’
• B. ‘W’
• C. ‘X’
• D. ‘Y’

Answer 1

The correct option is A

‘V’

The explanation for correct options:

1. The total energy required to release an electron from an isolated atom is called Ionisation energy. Elements with half-filled and fully filled orbitals have high ionisation energy.
2. Ionisation energy increases from left to right across a period.

Writing the electronic configuration for the elements V, W, X, and Y.

• V (10) = 1s²2s²2p⁶
• V (10) = [He] 2s² 2p⁶

• W (20) = 1s²2s²2p⁶3s²3p⁶4s²
• W (20) = [Ar] 4s²

• X (30) = 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰
• X (30) = [Ar] 3d¹⁰ 4s²

• Y (40) = 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d²
• Y (40) = [Kr]4d²5s²

Considering both orbital stability and trend across the period, the increasing order of ionisation energy is Y< W< X< V.

So, Option ‘a’ is correct. Thus, ‘V’ has the highest ionisation energy.

The explanation for incorrect options:

• Element with atomic number 40 has an incomplete d orbital. So, it will have the least ionisation energy.
• Elements with atomic numbers 30 and 40, though full-filled orbitals are located on the left side of the periodic table compared to the element with atomic number 10.