A mixed oxide of iron and chromium, `FeO.Cr_2O_3` is fused with sodium carbonate in the presence of air to form a yellow compound (A). On acidification, the compound (A) forms an orange coloured compound (B) which is a strong oxidising agent. Identify the compounds (A) and (B) .

Explanation

Since the inert pair effect is very prominent in Bi, therefore, its +5 oxidation state in much less stable than its +3 oxidation state. In other words, bismuth in the pentavalent state can easily accept two electrons and thus gets reduced to trivalent bismuth.
`Bi^(5+) + 2e^(-) to Bi^(3+)`
Therefore , it acts as a strong oxidising agent .