Question -
Answer -
Whenan alkaline earth metal is heated, the valence electrons get excited to ahigher energy level. When this excited electron comes back to its lower energylevel, it radiates energy, which belongs to the visible region. Hence, thecolour is observed. In Be and Mg, the electrons are strongly bound. The energyrequired to excite these electrons is very high. Therefore, when the electronreverts back to its original position, the energy released does not fall in thevisible region. Hence, no colour in the flame is seen.