The mass flux of species $$ in a multicomponent mixture is given by

Show that

$j_{{?}_{?}}()=n_{{?}_{?}}()-{}_{}{\displaystyle \underset{=1}{\overset{N}{}}}{n}_{{?}_{?}}()$;$,{\displaystyle \underset{=1}{\overset{N}{}}}{j}_{{?}_{?}}()=0$