Write in column B and C the expression and unit of physical quantity of column A$,$ in terms of potential $\frac{O}{?},$ velocity $v_i,$ concentration $c_i,$ charge number, $z_i,$ molar flux $N_i$ mobility $u_i$ and Faraday constant $F($e$.$g$.$ first row if filled$).$

$\backslash$table$[[$A: Physical quantity,B: Expression,C: Unit$],[$Electric field, $E_f,-$grad$\frac{O}{?},\frac{V}{m}$