Q.Which one of the following is strongest acid?

The oxoacid strength order is HClO4 > HClO3 > HClO2 > HClO, so the conjugate base of the weakest acid, ClO^-, is the strongest base.

For chlorine oxoacids, acid strength increases with the number of oxygen atoms (more oxygens stabilise the anion by spreading the negative charge):

HClO4 > HClO3 > HClO2 > HClO (decreasing acid strength)

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Acid strength of chlorine oxoacids rises with the number of terminal O atoms / oxidation state of Cl: HOCl < HClO2 < HClO3 < HClO4. Correct option (c).

For oxoacids of the same central halogen, acid strength increases as more oxygen atoms are attached, because they withdraw electron density and stabilise the conjugate base (anion) by spreading the negative charge over more oxygens.

• HOCl (Cl = +1) weakest
• HClO2 (Cl = +3)
• HClO3 (Cl = +5) …

Acid strength of chlorine oxoacids increases with the number of oxygen atoms bonded to chlorine: $HClO < HClO_2 < HClO_3 < HClO_4$.

All four acids have the general form $HOClO_n$ with the ionisable proton on an oxygen bonded to Cl. As the number of oxygen atoms attached to the central Cl atom increases:

1. The oxidation state of Cl increases (+1 in HClO, +7 in $HClO_4$), so Cl pulls electron density more strongly (higher effective electronegativity / -I effect), weakening the O-H bond and making the proton easier to release. …

Fluorine is the most electronegative element and shows only the -1 (and 0) state, so it forms just one oxyacid, HOF.

Because fluorine is more electronegative than oxygen, it cannot take a positive oxidation state in an oxyacid; it forms only hypofluorous acid, HOF, where fluorine is still effectively in a -1 state. Thus F2 gives only one oxyacid.

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Among HClO, HClO2, HClO3, HClO4, acidity increases with the number of non-hydroxyl (terminal) oxygens, so HClO4 is strongest.

For the oxoacids of chlorine, acid strength increases as the oxidation state of chlorine (and the number of terminal oxygen atoms) increases. More terminal O atoms withdraw electron density and stabilise the conjugate base by spreading the negative charge (reson …