Which of the following is the green coloured powder produced when ammonium dichromate is used in fireworks?

Which of the following are used as catalysts in petroleum cracking?

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.

The oxoanion in which the oxidation state of the central atom is same as its group number in the periodic table is

$Cu^{2+}$ aqueous solution has . . . . . . colour.

Fill in the blanks:
$(1)$ ......... acid is added to perform titrations with $KMnO_4$ and $K_2Cr_2O_7$.
$(2)$ Crystals of potassium dichromate are of ......... color,while crystals of potassium chromate are of ......... color.
$(3)$ The color of $MnO_4^{2-}$ is ......... and the color of $MnO_4^-$ is ......... .