Arrange the following oxyacids of sulphur in increasing order of the (average) oxidation state of sulphur: $H X_{2} S X_{2} O X_{3}$ , $H X_{2} S X_{2} O X_{4}$ , $H X_{2} S X_{2} O X_{6}$ , $H X_{2} S X_{2} O X_{7}$ .

A $H X_{2} S X_{2} O X_{4} < H X_{2} S X_{2} O X_{3} < H X_{2} S X_{2} O X_{6} < H X_{2} S X_{2} O X_{7}$
B $H X_{2} S X_{2} O X_{4} < H X_{2} S X_{2} O X_{3} < H X_{2} S X_{2} O X_{7} < H X_{2} S X_{2} O X_{6}$
C $H X_{2} S X_{2} O X_{3} < H X_{2} S X_{2} O X_{4} < H X_{2} S X_{2} O X_{6} < H X_{2} S X_{2} O X_{7}$
D $H X_{2} S X_{2} O X_{3} < H X_{2} S X_{2} O X_{4} < H X_{2} S X_{2} O X_{7} < H X_{2} S X_{2} O X_{6}$

Answer: C

With H = +1 and O = -2:

H X_{2} S X_{2} O X_{3}

gives

2 + 2 x - 6 = 0

x = + 2

;

H X_{2} S X_{2} O X_{4}

gives

x = + 3

;

H X_{2} S X_{2} O X_{6}

gives

x = + 5

;

H X_{2} S X_{2} O X_{7}

gives

x = + 6

. The order is therefore as in the first option.