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

How many ions liberate $H_2$ gas with dilute acids among the given species:
$Mn^{2+}, Cr^{3+}, Cr^{2+}, Zn^{2+}, Cu^{2+}, Sc^{3+}, Hg^{2+}$

Which of the following compounds does not react with cold and dil. $HNO_3$?

Iron is rendered passive by the action of

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 ........

The highest oxidation state of manganese in fluorides is $+4$ $(MnF_4)$, but the highest oxidation state in oxides is $+7$ $(Mn_2O_7)$, because