Explanation

$\lbrack E\rbrack = \left\lbrack ML^{2}T^{- 2} \right\rbrack,\lbrack m\rbrack = \lbrack M\rbrack,\lbrack l\rbrack = \lbrack ML^{2}T^{- 1}\rbrack$ and $\lbrack G\rbrack = \left\lbrack M^{- 1}L^{3}T^{- 2} \right\rbrack$ Substituting the dimensions of above quantities in the given formula: $\frac{El^{2}}{m^{5}G^{2}}\frac{\left\lbrack ML^{2}T^{- 2} \right\rbrack\left\lbrack ML^{2}T^{- 1} \right\rbrack^{2}}{\left\lbrack M^{5} \right\rbrack\left\lbrack M^{- 1}L^{3}T^{- 2} \right\rbrack^{2}} = \frac{M^{3}L^{6}T^{- 4}}{M^{3}L^{6}T^{- 4}} = \lbrack M^{0}L^{0}T^{0}\rbrack$