The ionisation constant of an acid, Ka is the measure of strength of an acid. The Ka values of acetic acid, hypochlorous acid and formic acid are 1.74×10-5, 3.0×10-8 and 1.8×10-4 respectively. Which of the following orders of pH of 0.1 mol dm-3 solutions of these acids is correct?

(1) Acetic acid > hypochlorous acid > formic acid

(2) Hypochlorous acid > acetic acid > formic acid

(3) Formic acid > hyochlorous acid > acetic acid

(4) Formic acid > acetic acid > hypochlorous acid

(4)  HINT: Ka α  acidity  α  1pH
 
As the acidity or Ka value increases, pH decreases, thus, the order pH value of the acids is
Hypochlorous acid(3.8×10-8) < acetic acid(1.74×10-5) < formic acid(18×10-4)