Amphoteric oxide$(s)$ of $Mn$ is/are:

Indicate the steps in the preparation of:
$(i)$ $K_2Cr_2O_7$ from chromite ore.
$(ii)$ $KMnO_4$ from pyrolusite ore.

Chrome yellow is chemically known as

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 ......... .

On heating a mixture of common salt and $K_{2}Cr_{2}O_{7}$ with concentrated $H_{2}SO_{4}$, a gas is evolved. The formula of the gas evolved and the oxidation state of the central metal atom in the gas, respectively, are:

Which compound is formed when iron reacts with carbon?