The ionisation cosntabnt of an acid, `K_(a)` is the meaure of strength of an acid. The `K_(a)` values of acetic acid, hypochlorous acid and formic acid are `1.74xx10^(-5)`, `3.0xx10^(-8)` and `1.8xx10^(-4)` respectively. Which of the following orders of ph of `0.1` mol `dm^(-3)` solutions of these acids is correct ?

Options

A. Acetic acid `gt` hypochlorous acid `gt` formic acid
B. Hypochlorous acid `gt` acetic acid `gt` formic acid
C. Formic acid `gt` hypochlorous acid ` gt` acetic acid
D. Formic acid `gt` acetic acid `gt` hypochlorous acid

Answer

D

Explanation

As the acidity or`K_(a)` value increase , pH decreases , thus the order of pH value of the acids is
`underset ((3.8 xx10^(-8)))("Hypochlorous acid") lt underset ((1.74 xx 10^(-5))) "Acetic acid "lt underset ((1.8 xx 10^(4))) " Formic acid "`