Identify the number of amphoteric species amongst the following :

${\mathrm{Mn}}_2{\mathrm{O}}_7,{\mathrm{CrO}}_3,{\mathrm{V}}_2{\mathrm{O}}_5,{\mathrm{V}}_2{\mathrm{O}}_4,{\mathrm{V}}_2{\mathrm{O}}_3,\mathrm{CrO},{\mathrm{Fe}}_2{\mathrm{O}}_3$

An amphoteric oxide is ${\mathrm{V}}_2{\mathrm{O}}_5$. It disintegrates slowly in water, unlike most metal oxides, and produces a pale yellow, acidic solution. As a result, when ${\mathrm{V}}_2{\mathrm{O}}_5$ interacts with powerful non-reducing acids, solutions containing the light yellow salts with dioxovanadium(V) centres are produced.

${\mathrm{V}}_2{\mathrm{O}}_5$  is amphoteric