$KMnO_4$ decomposes on heating at $513 \ K$ to form $O_2$ along with

Fill in the blanks:
$1.$ The copper layer on copper coins in the $UK$ is .......... .
$2.$ Copper-silver coins in the $UK$ are an alloy of ............ .
$3.$ The catalyst used for the oxidation of $SO_2$ to $SO_3$ is ......... .

Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing $pH$ on a solution of potassium dichromate?

The oxidising ability of the given anions follows the order:

Which from the following is the general formula of the compound obtained when lanthanoid $(Ln)$ reacts with carbon at elevated temperature?

The yellow colour solution of $Na_2CrO_4$ changes to orange-red on passing $CO_2$ gas due to the formation of