JEE Main 2023 · 15 April · morning · Numerical answer · +4 / −0

The total number of isoelectronic species from the given set is ___________.
O²⁻, F⁻, Al, Mg²⁺, Na⁺, O⁺, Mg, Al³⁺, F

Answer and solution

Answer 5

Solution

Chemistry ma’am · 3 steps

Count the electrons in every species first, then see which count repeats the most.

  1. What isoelectronic means. Isoelectronic species have the same total number of electrons. Start from the atomic number Z. Add one electron for each negative charge and remove one for each positive charge.

    electrons = Z - (charge)

  2. Atomic numbers. O is 8, F is 9, Na is 11, Mg is 12 and Al is 13. So, for example, O²⁻ has 8 + 2 = 10 electrons and O⁺ has 8 - 1 = 7.
    ElectronsSpeciesWorking
    10O²⁻, F⁻, Na⁺, Mg²⁺, Al³⁺8+2, 9+1, 11-1, 12-2, 13-3
    13Alneutral atom, Z = 13
    12Mgneutral atom, Z = 12
    9Fneutral atom, Z = 9
    7O⁺8 - 1
  3. So. Only the 10-electron group has more than one member. O²⁻, F⁻, Na⁺, Mg²⁺ and Al³⁺ all have the neon configuration, so the answer is 5.

The idea to keep. For isoelectronic questions, write the electron count next to every species. Negative charge adds electrons and positive charge removes them. Ions around neon usually form the 10-electron set.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Atomic Structure

Asked about 170 times in JEE Main since 2020. This question is from 2023.