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Which oxide of $Mn$ is acidic in nature?

On heating $KMnO_4$,one among the following is not formed:

When borax is heated with cobalt oxide,which of the following compounds produces a blue-colored bead?

The amphoteric oxide of Vanadium $(V)$ is $V_2O_5$. It reacts with alkali to form an oxoion '$X$' and with acid to form an oxoion '$Y$'. The oxidation states of '$V$' in '$X$' and '$Y$' are respectively:

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