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NEET CHEMISTRYMedium

Which of the following species contains an equal number of σ\sigma and π\pi bonds?

A

HCO3−HCO_3^-

B

XeO4XeO_4

C

(CN)2(CN)_2

D

CH2(CN)2CH_2(CN)_2

Step-by-Step Solution

  1. Analyze XeO4XeO_4: Xenon (Xe) has 8 valence electrons. It forms double bonds with four oxygen atoms to achieve a stable tetrahedral geometry. Each double bond consists of 1 σ\sigma bond and 1 π\pi bond.
  • Total σ\sigma bonds = 4
  • Total π\pi bonds = 4
  • Result: Equal number of σ\sigma and π\pi bonds .
  1. Analyze other options:
  • HCO3−HCO_3^- (Bicarbonate ion): The structure is HO−C(=O)−O−HO-C(=O)-O^-. It contains 4 σ\sigma bonds (C-O, C=O, C-O, O-H) and 1 π\pi bond (in C=O). (4σ,1π4\sigma, 1\pi)
  • (CN)2(CN)_2 (Cyanogen): The structure is N≡C−C≡NN \equiv C - C \equiv N. It contains 3 σ\sigma bonds (one C-C, two C-N) and 4 π\pi bonds (two in each C≡NC\equiv N triple bond). (3σ,4π3\sigma, 4\pi) .
  • CH2(CN)2CH_2(CN)_2 (Malononitrile): The structure is NC−CH2−CNNC-CH_2-CN. It contains 6 σ\sigma bonds (two C-H, two C-C, two C-N) and 4 π\pi bonds (two in each C≡NC\equiv N). (6σ,4π6\sigma, 4\pi)
  1. Conclusion: Only XeO4XeO_4 has an equal number of sigma and \pi bonds.
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