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JEE · NEET Previous Year Question

Which one of the following species does not exist under normal conditions ?

Topic: NEET PYQ

Answer: B. Full step-by-step solution below.

  1. ABe2+
  2. BBe2
  3. CB2
  4. DLi2

Correct answer: B

Solution

(b) Molecules with zero bond order, do not exist.
(a) Be2+ (4 + 4 – 1 = 7) = σ1s2, σ1s2, σ2s2, σ2s1
BO = = 0.5
(b) Be2 (4 + 4 = 8) = σ1s2, σ1s2, σ2s2, σ2s2
BO = = 0
(c) B2 (5 + 5 = 10) = σ1s2, σ1s2, σ2s2, σ2s2, π2px1 ≈ π2py1
BO = = 1
(d) Li2 (3 + 3 = 6) = σ1s2, σ1s2, σ2s2
BO = = 1
Thus, Be2 does not exist under normal conditions.

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