When two different halogens react with each other, interhalogen compounds are formed. They can be assigned general compositions as \(XX'\), \(XX'_3\), \(XX'_5\) and \(XX'_7\), where \(X\) is a halogen of larger size and \(X'\) of smaller size and \(X\) is more electropositive than \(X'\). As the ratio between radii of \(X\) and \(X'\) increases, the number of atoms per molecule also increases.
On the basis of above passage, answer the questions
Shape of \(XX'_5\) compound is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Square pyramidal
The shapes of interhalogen compounds follow from VSEPR theory. In XX′5 (e.g. \( \ce{BrF5} \), \( \ce{IF5} \), \( \ce{ClF5} \)), the central atom X has 7 valence electrons; five are used in bonds with X′ and the remaining two form one lone pair:
5 bond pairs + 1 lone pair = 6 electron pairs → octahedral arrangement (sp3d2)
One position of the octahedron is taken by the lone pair, so the five X′ atoms form a square pyramid.
Why the other options are incorrect
Option (1) Trigonal Planar — Incorrect. Three bond pairs and no lone pair (e.g. \( \ce{BF3} \)); no interhalogen has this shape.
Option (2) Square Planar — Incorrect. Four bond pairs and two lone pairs (e.g. \( \ce{XeF4} \), \( \ce{ICl4^{-}} \)); XX′5 has five bonds.
Option (3) Bent T shape — Incorrect. Three bond pairs and two lone pairs; this is the shape of XX′3 (e.g. \( \ce{ClF3} \)), not XX′5.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Interhalogen Compounds – “When two different halogens react with each other, interhalogen compounds are formed. They can be assigned general compositions as XX′, XX′3, XX′5 and XX′7 where X is halogen of larger size and X′ of smaller size and X is more electropositive than X′. … Their molecular structures are very interesting which can be explained on the basis of VSEPR theory (Example 7.19). The XX′3 compounds have the bent ‘T’ shape, XX′5 compounds square pyramidal and IF7 has pentagonal bipyramidal structures (Table 7.11).”