What is the oxidation number of As in the compound $\mathrm{K}{\left({\mathrm{NH}}_4\right)}_2{\mathrm{AsO}}_4\cdot 6{\mathrm{H}}_2\mathrm{O}$?

The oxidation number of given compound;

$\stackrel{+1}{\mathrm{K}}\left({\stackrel{+2}{\mathrm{NH}}}_4\right)\stackrel{+5}{{ }_2\mathrm{A}}2\mathrm{s}{\stackrel{-8}{\mathrm{O}}}_4\cdot 6{\stackrel{0}{\mathrm{H}}}_2\mathrm{O}$

Thus, the oxidation number of As in the compound $\mathrm{K}{\left({\mathrm{NH}}_4\right)}_2{\mathrm{AsO}}_4\cdot 6{\mathrm{H}}_2\mathrm{O}$ is +5.