Sodium vapour lamps glow with yellow colour. This is due to A. sublimation of sodium to emit yellow colour B. The emission of excess energy absorbed by sodium atoms, in the yellow region of the spectrum C. The low ionisation energy of sodium D. Its ability to absorb all other colours except yellow

The correct answer is: B. The emission of excess energy absorbed by sodium atoms, in the yellow region of the spectrum.

When sodium atoms are heated, they absorb energy from the heat source. This energy causes the electrons in the sodium atoms to move to higher energy levels. When the electrons fall back down to their original energy levels, they

emit light. The light that is emitted is in the yellow region of the spectrum, which is why sodium vapor lamps glow with yellow light.

Option A is incorrect because sublimation is the process of a solid turning directly into a gas without passing through a liquid phase. This is not what happens in sodium vapor lamps.

Option C is incorrect because the low ionization energy of sodium does not cause the sodium atoms to emit light. The low ionization energy of sodium does make it easier for the electrons in the sodium atoms to be excited to higher energy levels, but it is the emission of excess energy that causes the sodium atoms to emit light.

Option D is incorrect because sodium vapor lamps do not absorb all other colors except yellow. They absorb all colors of light, but they only emit light in the yellow region of the spectrum.