An element `A` in a compound `ABD` has oxidation number `A^(n-)`. It is oxidised by `Cr_(2)O_(7)^(2-)` in acid medium. In the experiment `1.68xx10^(-3)` moles of `K_(2)Cr_(2)O_(7)` were used for `3.26xx10^(-3)` moles of `ABD`. The new oxidation number of `A` after oxidation is:

Options

A. `3`
B. `3-n`
C. `n-3`
D. `+n`

Answer

B

Explanation

`A^(n-)rarrA^(a+)+(a+n)e`
`6e+(Cr^(6+))_(2)rarr2Cr^(3+)`
Also Meq.of `A="Meq.of" K_(2)Cr_(2)O_(7)`
`3.26xx10^(-3)(a+n)=1.68xx10^(-3)xx6`
`:. a+n=3` or `a=3-n`