$ \uparrow Y_{(g)} \xleftarrow{KI} CuSO_4 \xrightarrow{dil. H_2SO_4} X (\text{Blue colour}) $. $X$ and $Y$ are:

The orange colour of $K_2Cr_2O_7$ and purple colour of $KMnO_4$ is due to

Stainless steel is non-corrosive. This character is more prominent in

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 first transition series metal $M$ has the highest enthalpy of atomisation in its series. One of its aquated ion $(M^{n+})$ exists in green colour. The nature of the oxide formed by the above $M^{n+}$ ion is $:$

Which one of the following,when dissolved in water,gives a coloured solution in a nitrogen atmosphere?