Out of Mg, Be, Ca, Sr, and Ba, number of elements which do not impart any colour to the flame is ___ .

Out of given elements Be and Mg do not impart any color to flame because they have small atomic size and high ionization energies when compared to other alkaline earth metals. The energy of flame is not sufficient to excite the electrons of Be and Mg to higher energy level. Hence, Be and Mg do not give any color in Bunsen flame.