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NEET Chemistry QUESTION #7407
Question 1
Which is the correct order for the first ionisation potential (IP₁)?
  • \(\text{Na} > \text{Al}\)
  • \(\text{Mg} > \text{Al}\)✔️
  • \(\text{Ga} > \text{Ca}\)
  • \(\text{Mg} > \text{Be}\)
Correct Answer Explanation
IE₁ irregularities:
Generally IE₁ increases left to right, but Al (3p¹) has lower IE₁ than Mg (3s²) because:
  • Mg has a full 3s² subshell (extra stability)
  • Al's 3p electron is shielded by 3s electrons and easier to remove
Therefore \(\text{Mg} > \text{Al}\) is a correct and expected inequality. This is one of the classic exceptions to the smooth IE trend across period 3.