$A$ metal $M$ which is not affected by strong acids like conc. $HNO_3$,conc. $H_2SO_4$ and conc. solutions of alkalies like $NaOH$,$KOH$ forms $MCl_3$,which finds use for toning in photography. The metal $M$ is:

Which substance is used to produce very low temperatures by magnetic effects?

The orange colour of $K_2Cr_2O_7$ and purple colour of $KMnO_4$ is due to

The purple colour of $KMnO_4$ is due to the transition:

Identify the reactions in which dichromate acts as an oxidising reagent.
$I$. $Cr_2O_7^{2-} + 6Fe^{2+} + 14H^{+} \longrightarrow 2Cr^{3+} + 6Fe^{3+} + 7H_2O$
$II$. $Cr_2O_7^{2-} + 2OH^{-} \longrightarrow 2CrO_4^{2-} + H_2O$
$III$. $Cr_2O_7^{2-} + 6I^{-} + 14H^{+} \longrightarrow 2Cr^{3+} + 3I_2 + 7H_2O$
$IV$. $Na_2Cr_2O_7 + 2KCl \longrightarrow K_2Cr_2O_7 + 2NaCl$

Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with:
$(i)$ iodide
$(ii)$ iron $(II)$ solution and
$(iii)$ $H_{2}S$