Explanation:

Emission spectrum refers to the spectrum of light emitted by a substance that has been excited by some external energy source. Sodium vapour lamp is a common example of an emission spectrum. The lamp consists of a tube containing sodium vapour at low pressure, with electrodes at either end. When an electric current is passed through the tube, the sodium atoms become excited and emit light. This light has a characteristic wavelength that is determined by the energy levels of the sodium atoms.

The spectrum obtained from a sodium vapour lamp is an example of an emission spectrum because it is produced by the emission of light from excited sodium atoms. This spectrum consists of a series of bright lines on a dark background, with each line corresponding to a particular wavelength of light. The wavelengths of these lines are characteristic of the element sodium and can be used to identify it.

The other options mentioned in the question are not correct. Band spectrum refers to a spectrum in which the energy levels of the atoms or molecules are closely spaced, resulting in a series of closely spaced lines that appear as a band. Continuous spectrum, on the other hand, refers to a spectrum that contains all wavelengths of light within a certain range. Absorption spectrum refers to a spectrum in which certain wavelengths of light are absorbed by a substance, resulting in dark lines on a bright background.

In conclusion, the spectrum obtained from a sodium vapour lamp is an example of an emission spectrum because it is produced by the emission of light from excited sodium atoms. This spectrum consists of bright lines on a dark background, with each line corresponding to a particular wavelength of light that is characteristic of the element sodium.