Which of the following statements is not correct?

Fusion of $MnO_2$ with $KOH$ in the presence of air or an oxidizing agent like $KNO_3$ forms a colored compound. Identify the product and its color.

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 ......... .

Which of the following is a highly corrosive salt?

Calomel is the name of

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 $MnO_2$.