JEE Main · 2005 · 08 May 2005 · Offline · Classification of Elements and Periodicity

Of the following sets which one does NOT contain isoelectronic species?

Answer: (C)

Solution

Isoelectronic species must have identical electron counts, so we tally each set. In the carbonate-like trio the counts come to

SO X_{3} X^{2 -}

with

16 + 24 + 2 = 42

electrons, against

CO X_{3} X^{2 -}

with

6 + 24 + 2 = 32

and

NO X_{3} X^{-}

with

7 + 24 + 1 = 32

. Sulphite stands apart at

42

electrons while the other two agree at

32

, so that is the set which is not isoelectronic, the remaining sets all coming out equal.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option