Generally,metal ions and their salts are coloured due to the presence of unpaired electrons in the metal ions. Which of the following compounds is coloured?

Chromite ore $\xrightarrow{Na_2CO_3 + O_2} A$ $\xrightarrow[NaOH]{H_2SO_4} B$. Which of the following is correct?

Which alloy is used for making coins?

$Fe_2Cr_2O_4 + Na_2CO_3 + O_2$ $\xrightarrow{\text{Fusion}} [X]$ $\xrightarrow[H_2O]{H^{+}} [Y]$ $\xrightarrow{H_2O_2/H^{+}} [Z]$
Which of the following statements is true for the compounds $[X]$,$[Y]$,and $[Z]$?

Among $Co^{3+}$,$Ti^{2+}$,$V^{2+}$ and $Cr^{2+}$ ions,one if used as a reagent cannot liberate $H_{2}$ from dilute mineral acid solution,its spin-only magnetic moment in gaseous state is $.....$ $B.M.$ (Nearest integer)

When an oxide of manganese $(A)$ is fused with $KOH$ in the presence of an oxidising agent and dissolved in water,it gives a dark green solution of compound $(B)$. Compound $(B)$ disproportionates in neutral or acidic solution to give purple compound $(C)$. An alkaline solution of compound $(C)$ oxidises potassium iodide solution to a compound $(D)$ and compound $(A)$ is also formed. Identify compounds $A$ to $D$ and also explain the reactions involved.