JEE Main 2023 · 1 February · evening · Single correct · +4 / −1
O-O bond length in H₂ O₂ is X than the O-O bond length in F₂ O₂. The O-H bond length in H₂ O₂ is Y than that of the O-F bond in F₂ O₂.
Choose the correct option for X and Y from those given below :
- (a) X - shorter, Y - longer
- (b) X - longer, Y - shorter
- (c) X - shorter, Y - shorter
- (d) X - longer, Y - longer
Answer and solution
Answer (b) X - longer, Y - shorter
Solution
Chemistry ma’am · 3 steps
In O₂F₂ the O–O bond is almost a double bond, and the O–F bonds pay for it by getting long.
- O–O in H2O2. In H₂O₂ the two oxygens share a plain single bond, so the O–O bond is long, about 147.5 pm in the gas phase.
- O–O in O2F2. Fluorine is so electronegative that each O–F bond is weak and partly ionic. Resonance forms like F⁻ [F-O=O]⁺ give the O–O bond strong double-bond character, so it shrinks to about 121.7 pm, close to the O=O in O₂. Because the O–F bonds are partly ionic, they come out unusually long, about 157.5 pm.
Bond H₂O₂ O₂F₂ Comparison O–O about 147.5 pm (single) about 121.7 pm (near double) H₂O₂ is longer, so X = longer O–H vs O–F O–H about 95 pm O–F about 157.5 pm O–H is shorter, so Y = shorter - So. X is longer and Y is shorter, which is option (b).
The idea to keep. When very electronegative atoms sit on a peroxide link, the O–O bond tightens toward a double bond and the bonds to those atoms weaken and stretch. Short O–O comes with long O–X.
Answer from the NTA final answer key. Solution by PrepWiser.