Use average oxidation numbers of sulphur. Select ALL correct statements about thiosulphate $S X_{2} O X_{3} X^{2 -}$ .

AThe average oxidation number of S in $S X_{2} O X_{3} X^{2 -}$ is +2
BThe n-factor of $S X_{2} O X_{3} X^{2 -}$ in its oxidation to $S X_{4} O X_{6} X^{2 -}$ by $I X_{2}$ is 1
CThe n-factor of $S X_{2} O X_{3} X^{2 -}$ in its oxidation to $SO X_{4} X^{2 -}$ by $Cl X_{2}$ is 8
DThe average oxidation number of S in $S X_{4} O X_{6} X^{2 -}$ is +3

Answer: A, B, C

S X_{2} O X_{3} X^{2 -}

: 2x - 6 = -2, so x = +2. In

S X_{4} O X_{6} X^{2 -}

: 4x - 12 = -2, so x = +2.5 (not +3), making statement 4 false. For

S X_{2} O X_{3} X^{2 -}

S X_{4} O X_{6} X^{2 -}

, 2 thiosulphate lose 2 electrons in total (2 x 2 -> 4 x 2.5), so n-factor = 1. To sulphate, each S goes +2 to +6, so n-factor = 2 x 4 = 8.