Assertion A: The first ionisation enthalpy decreases across a period.

Reason R: The increasing nuclear charge outweighs the shielding across the period.

Question

Assertion A: The first ionisation enthalpy decreases across a period.

Reason R: The increasing nuclear charge outweighs the shielding across the period.

Canvas Classes · Accepted Answer

Strategy:
 First ionization enthalpy () represents the energy required to remove the most loosely bound electron. This is governed by the balance between nuclear attraction and electronic shielding (electron-electron repulsion).

Step 1: Evaluate Assertion (A)
- Across a period, atomic size decreases and effective nuclear charge () increases. This makes it harder to remove an electron.
- Therefore,  generally increases across a period. (False)

Step 2: Evaluate Reason (R)
- Across a period, elec

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