Beryllium and magnesium to not give colour to flame whereas other alkaline earth metals do so. Why ?

Explanation

Beryllium and magnesium have high ionization enthalpy. The electrons in the outermost shell of these elements are two strongly bound and will not get excited to higher energy levels by Bunsen burner flame. Hence Beryllium and magnesium to dnot give colour to flame. While in ofhter alkaline earth metals, ionization enthalpy is lower. So, electrons in the outer most shell are easily excited to higher energy levels by the flame. Hence, they give characteristic colours to the flame.