$Zn_{(s)} + CuSO_{4(aq)} \rightarrow ZnSO_{4(aq)} + Cu_{(s)}$ is an example of which type of process?

Iron is dropped in dilute $HNO_3$,it gives:

Consider the following reaction:
$MnO_2 + KOH + O_2 \rightarrow A + H_2O$
Product '$A$' in neutral or acidic medium disproportionates to give products '$B$' and '$C$' along with water. The sum of spin-only magnetic moment values of '$B$' and '$C$' is . . . . . $BM$. (nearest integer)
(Given atomic number of $Mn$ is $25$)

In basic medium,$CrO_{4}^{2-}$ oxidises $S_{2}O_{3}^{2-}$ to form $SO_{4}^{2-}$ and itself changes into $Cr(OH)_{4}^{-}$. The volume of $0.154 \ M \ CrO_{4}^{2-}$ required to react with $40 \ mL$ of $0.25 \ M \ S_{2}O_{3}^{2-}$ is ........... $mL$ (Rounded-off to the nearest integer).

Which of the following reactions represents a redox reaction involving water?

In the following reaction,identify the oxidation states of the underlined phosphorus atoms in the products formed by complete hydrolysis at $R.T.$:
$H_4\underline{P}_2O_6 + H_2O \longrightarrow H_3PO_3 + H_3PO_4$