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NEET Chemistry QUESTION #7403
Question 1
Among elements with electronic configurations Ne[3s²3p¹], Ne[3s²3p³], Ne[3s²3p²], and Ar[3d¹⁰4s²4p³], which may have the highest ionisation energy?
  • Ne[3s²3p¹]
  • Ne[3s²3p³]✔️
  • Ne[3s²3p²]
  • Ar[3d¹⁰4s²4p³]
Correct Answer Explanation
Ne[3s²3p³] corresponds to phosphorus — with a half-filled 3p³ subshell. Half-filled subshells have extra stability (exchange energy + symmetry), so removing an electron requires more energy. This gives P a higher IE₁ than S (next element).

Ne[3s²3p¹] = Al, Ne[3s²3p²] = Si, Ne[3s²3p³] = P, Ar[3d¹⁰4s²4p³] = As. Among these, P has the highest IE₁ due to half-filled stability.