Given the species:${\mathrm{Mn}}^{3+},{\mathrm{Co}}^{3+},{\mathrm{Ti}}^{2+},{\mathrm{V}}^{2+},{\mathrm{Cr}}^{2+},{\mathrm{Fe}}^{2+}$

(a) Find the number of species which are strong oxidising agent = X

(b) Find the number of species which are strong reducing agents and will liberate hydrogen from dilute acid = Y

Hence, find the value of 3X - Y.