Question

Ba and mg do not impart colour to the flame while other members of 2 explain

Answer 1

Beryllium and magnesium atoms are smaller in size and their electrons are strongly bound to the nucleus. They need large amounts of energy for excitation of electrons to higher energy levels which is not available in the bunsen flame. So they do not impart colour to the flame.

Answer 2

Ba imparts apple green colour to the flame whereas Mg and Be cannot because they have a stable lattice structure and cannot excite their electron to higher orbits to impart colour.