Which of the following statements about chromium species are correct?

AAcidic $H X_{2} O X_{2}$ is the reagent for oxidising $Cr X^{3 +}$ to $CrO X_{4} X^{2 -}$ in the group III scheme
BChromium has oxidation state $+ 6$ in both $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$
CAcidifying chromate to dichromate is not a redox reaction
DIn $CrO X_{5}$ chromium is in oxidation state $+ 6$ and the compound has two peroxo groups

Answer: B, C, D

Both chromate and dichromate are Cr(VI), the conversion

2 CrO X_{4} X^{2 -} + 2 H X^{+} Cr X_{2} O X_{7} X^{2 -} + H X_{2} O

involves no electron transfer, and

CrO X_{5}

has Cr(VI) with two

O X_{2} X^{2 -}

units. The oxidation of Cr(III) to chromate requires alkaline peroxide, not acidic, so the last statement is false.