How many moles of $K_2Cr_2O_7$ will be reduced by $1$ mole of $Sn^{2+}$ ions?

Which of the following is a redox reaction?

In which reaction is there a change in the oxidation state?

The reaction of bromine water with $SO_2$ produces .......

For the given redox reaction: $a MnO_4^{-} + b S_2 O_3^{2-} + H_2 O \longrightarrow x MnO_2 + y SO_4^{2-} + z OH^-$,the values of $a$ and $y$ respectively are:

What is the equivalent weight of hydrochloric acid in the given redox reaction $MnO_2 + 4HCl \to MnCl_2 + 2H_2O + Cl_2$?
If the molar mass of hydrochloric acid is $M$.