The colour imparted by $Co(II)$ compounds to glass is

Iodine is formed when potassium iodide reacts with a solution of

Highest fluoride and highest oxide of $Mn$ are respectively

Fusion of $MnO_2$ with $KOH$ in presence of $O_2$ produces a salt $W$. Alkaline solution of $W$ upon electrolytic oxidation yields another salt $X$. The manganese containing ions present in $W$ and $X$,respectively,are $Y$ and $Z$. Correct statement$(s)$ is (are)
$(1)$ $Y$ is diamagnetic in nature while $Z$ is paramagnetic
$(2)$ Both $Y$ and $Z$ are coloured and have tetrahedral shape
$(3)$ In both $Y$ and $Z$,$\pi$-bonding occurs between $p$-orbitals of oxygen and $d$-orbitals of manganese.
$(4)$ In aqueous acidic solution,$Y$ undergoes disproportionation reaction to give $Z$ and $MnO_2$.

The compounds formed when $KMnO_4$ is heated to $513 \ K$ are . . . . . .

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