SSC MTS 2024 PYQ — Question 55

The correct answer is  option 2  i.e.  Atomic radius .

Ionisation energy is the energy required to remove an electron from a neutral atom in its gaseous state.

Atomic radius refers to the size of an atom.

These two properties are inversely related:

• When atomic radius increases, the outer electrons are farther from the nucleus and less tightly held, making it easier to remove an electron → lower ionisation energy.

• Conversely, a smaller atomic radius means electrons are closer to the nucleus and more tightly bound → higher ionisation energy.

Thus, atomic radius is inversely related to ionisation energy. 

Incorrect Options :

• Electron affinity: Measures how much an atom wants to gain an electron; it doesn't have a direct inverse relationship with ionisation energy.

• Atomic mass: This affects isotopes and stability, but has no direct relation to ionisation energy.

• Electronegativity: Generally correlates directly with ionisation energy — elements that strongly attract electrons also tend to hold onto their own electrons tightly.