JEE Advanced levelSingle correct optionDifficulty 3 of 3cb030
Assertion (A): In SFX4 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.
ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
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.