JEE Main 2021 · 31 August · morning · Numerical answer · +4 / −0
The number of halogen/(s) forming halic (V) acid is ___________.
Answer and solution
Answer 3
Solution
Chemistry ma’am · 3 steps
A halic(V) acid needs the halogen at +5, so first ask which halogens can show a positive oxidation state.
- What halic(V) means. A halic(V) acid has the formula HXO₃, with the halogen X in the +5 oxidation state. So the halogen must be able to take a high positive oxidation state with oxygen.
- Fluorine is different. Fluorine is the most electronegative element, so it shows only the -1 state in its compounds. It also has no d orbitals in its valence shell. Its only oxoacid is HOF, so it has no +5 acid.
Halogen Can it show +5? Halic(V) acid F No, only -1 none (only HOF exists) Cl Yes HClO₃, chloric acid Br Yes HBrO₃, bromic acid I Yes HIO₃, iodic acid - So. Chlorine, bromine and iodine each form a halic(V) acid, and fluorine does not. The answer is 3.
The common slip: 4. Counting fluorine along with the other three gives 4. Fluorine has no positive oxidation state in its compounds, so it forms no HFO₃.
The idea to keep. Any oxoacid question in Group 17: drop fluorine first. It shows only -1 and forms just HOF. Cl, Br and I give the full series of oxoacids.
Answer from the NTA final answer key. Solution by PrepWiser.