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JEE Advanced levelSingle correct optionDifficulty 3 of 3cb030

Assertion (A): In the lone pair occupies an equatorial position of the trigonal bipyramid. Reason (R): An equatorial lone pair has only two bond pairs at 90 degrees to it, whereas an axial lone pair would have three.

  1. ABoth A and R are true and R is the correct explanation of A
  2. BBoth A and R are true but R is not the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: A

Lone pair-bond pair repulsion is strongest at 90 degrees. An equatorial position has 2 neighbours at 90 degrees, an axial position has 3, so the lone pair goes equatorial and the shape is see-saw. R correctly explains A.
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