Which of the following does not react with oxygen directly? $Zn$,$Ti$,$Pt$,$Fe$

The highest Mn fluoride is $MnF_4$ whereas the highest oxide is $Mn_2O_7$,because . . . . . . .

When $Cu^{2+}$ ion is treated with $KI$,a white precipitate is formed. Explain the reaction with the help of a chemical equation.

Consider the following transformation:
$2CuX_2 \xrightarrow{\text{Room temperature}} 2CuX + X_2 \uparrow$
Then $X^-$ can be:

Fill in the blanks:
$(a)$ The only $Mn$ halide compound that shows an oxidation state of $+7$ is ........
$(b)$ The $E^{\ominus}_{M^{II}/M}$ value is maximum negative for ........ in the $3d$ series.
$(c)$ Between $Cr^{2+}$ and $Fe^{2+}$,the stronger reducing agent is ........

For $Cr, Mn, Fe,$ and $Co$,the $E^{0}_{M^{3+}/M^{2+}}$ values are $-0.41, +1.57, +0.77,$ and $+1.97 \ V$ respectively. For which metal is the change in oxidation state from $+2$ to $+3$ the easiest?