The transition metal which forms a green compound in $+3$ oxidation state and a yellow-orange compound in $+6$ oxidation state is

$Fe(OH)_2$ is precipitated from $Fe(II)$ solutions as a white solid but turns dark green and then brown due to the formation of:

Where is potassium dichromate used?

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with $(i)$ iron $(II)$ ions,$(ii)$ $SO_2$,and $(iii)$ oxalic acid? Write the ionic equations for the reactions.

Which among the following statements is incorrect for manganate and permanganate ions?

How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore?