36 " mL of " 0.5 M `Br_(2)` solution when made alkaline undergoes complete disproportionation into `Br^(ɵ)` and `BrO_(3)^(ɵ)`. The resulting solution requried 45 " mL of " As (III) solution to reduce `BrO_(3)^(ɵ)` to `Br^(ɵ)`. Given that as (III) is oxidised to As (V), what is the molarity of As (III) solution?

Options

A. 0.2
B. 0.1
C. 0.4
D. 0.5

Answer

C

Explanation

`6 mmol Br_(2)-=2 mmol Br_(3)^(ɵ)`
`(36xx0.5)=(1)/(3)xx36xx0.5 mmol BrO_(3)^(ɵ)`
`BrO_(3)^(ɵ)+3As^(3+)+6H^(o+)toBr^(ɵ)+3As^(5+)+3H_(2)O`
`1 m" mol of "BrO_(3)^(ɵ)-=3 mmol As^(3+)`
`6.0 mmol BrO_(3)^(ɵ)-=mmol As^(3+)`
`(MAs^(3+)=(18)/(45)=0.4M)`