Question

Arrange the following elements in the decreasing order of their first ionisation energy.

• A. Boron (B)
• B. Carbon (C)
• C. Beryllium (Be)
• D. Oxygen (O)

Answer 1

These elements belong to the second period in the modern periodic table.
As we move from left to right across a period, atomic size decreases. This results in a greater pull on the electrons and therefore more energy is required to remove them.

The correct order of first ionisation energy would be:
O > C > B > Be