Why do Beryllium and Magnesium does not show color to the flame as other alkaline earth metals do?

Reason of alkaline earth metals to show color

• Alkali or alkaline earth metals impart color to the flame due to the excitation of electrons to a higher energy levels and then these electrons come back to the ground state.
• When they come back to ground state, energy is emitted as visible light and they show the complementary color in the flame test.

Reason for Beryllium and magnesium not showing color in the flame test:

• Both beryllium and magnesium atoms are having small size and higher effective nuclear charge.
• Consequently, it require high excitation energy for the emission of the radiation and hence they are not excited by the energy of the flame and thus, do not show any color in the flame test.