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
Interhalogen compounds are:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → More reactive than halogens except fluorine.
In general, interhalogen compounds are more reactive than halogens (except fluorine). The reason is the bond strength: the X–X′ bond in interhalogens is weaker than the X–X bond in halogens, except the F–F bond. Two different atoms of unequal size overlap less effectively, and the bond is also polar, so it breaks more easily. All of them undergo hydrolysis, e.g.
\( \displaystyle \ce{ICl + H2O -> HCl + HOI} \)
Fluorine is the exception because the F–F bond is unusually weak (lone pair repulsion in the small \( \ce{F2} \) molecule), so fluorine is more reactive than the interhalogens.
Why the other options are incorrect
Option (1) Inert in nature — Incorrect. Interhalogens are reactive compounds; they are used as fluorinating agents (\( \ce{ClF3} \), \( \ce{BrF3} \)) and react with water.
Option (2) Less reactive than halogens — Incorrect. The opposite is true, because the X–X′ bond is weaker than the X–X bond (except F–F).
Option (4) Product formed depends on the reaction conditions. — Incorrect. This describes their preparation (e.g. \( \ce{Cl2} \) + \( \ce{F2} \) gives ClF at 437 K but \( \ce{ClF3} \) at 573 K with excess \( \ce{F2} \)), not what interhalogen compounds are.
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 – “… Their chemical reactions can be compared with the individual halogens. In general, interhalogen compounds are more reactive than halogens (except fluorine). This is because X–X′ bond in interhalogens is weaker than X–X bond in halogens except F–F bond. All these undergo hydrolysis giving halide ion derived from the smaller halogen and a hypohalite (when XX′), halite (when XX′3), halate (when XX′5) and perhalate (when XX′7) anion derived from the larger halogen.”