Which one of the following metals will not reduce ${H_2}O$

The spin-only magnetic moment value of $M ^{3+}$ ion (in gaseous state) from the pairs $Cr ^{3+} / Cr ^{2+}$, $Mn ^{3+} / Mn ^{2}, Fe ^{3+} / Fe ^{2+}$ and $Co ^{3+} / Co ^{2+}$ that has negative standard electrode potential, is $B.M...........$ [Nearest integer]

The only cations present in a slightly acidic solutions are $Fe^{3+},\,Zn^{2+}$ and $Cu^{2+}$. The reagent that when added in excess to this solution would identify and separate $Fe^{3+}$ in one step is

$\operatorname{Zr}\,(\mathrm{Z}=40)$ and $\mathrm{Hf}\,(\mathrm{Z}=72)$ have similar atomic and ionic radii because of :

Spiegeleisen is an alloy of

Which of the following ionic species will impart colour to an aqueous solution