Find the total number of species which would undergo disproportionation in alkaline medium.

${\mathrm{NO}}_2,{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-},{\mathrm{Cl}}_2{\mathrm{O}}_6,{\mathrm{Br}}_2,{\mathrm{P}}_4,{\mathrm{S}}_8,{\mathrm{Al}}_2{\mathrm{O}}_3$

Non-metals undergo disproportionation in alkaline medium.

In an alkaline media, ${\mathrm{NO}}_2$disproportionally transforms into ${\mathrm{NNO}}_2$ and ${\mathrm{NNO}}_3$ .
${\mathrm{Cl}}_2{\mathrm{O}}_6$ disproportionally transforms into ${\mathrm{NaClO}}_2$ and ${\mathrm{NaClO}}_4$in an alkaline media.
In an alkaline media,${\mathrm{Br}}_2$ disproportionally forms $\mathrm{Br}$ and ${\mathrm{NaBrO}}_3$.
${\mathrm{P}}_4$ disproportionally reacts with an alkaline media to produce ${\mathrm{PH}}_3$and ${\mathrm{NaH}}_2{\mathrm{PO}}_2$.
In an alkaline media, ${\mathrm{S}}_8$ disproportionally transforms into ${\mathrm{H}}^{2-}$ and ${\mathrm{S}}_2{\mathrm{O}}_3$.
 

$\left[{\mathrm{NO}}_2,{\mathrm{Cl}}_2{\mathrm{O}}_6,{\mathrm{Br}}_2,{\mathrm{P}}_4,{\mathrm{S}}_8\right]$