Final answer:
The emission lines of an atom are found at the same wavelengths as its absorption lines, serving as a unique fingerprint for each element's presence in a sample and this finding forms the basis of spectroscopy in physics.
Step-by-step explanation:
The emission line for a given atom shows spectral features at the same location as in its absorption spectrum. When electrons in an atom absorb energy, they move to higher energy levels and produce absorption lines. Conversely, when electrons drop to lower energy levels, they emit energy and create emission lines. The key point here is that these transitions occur at specific and unique energy levels for each element, which correspond to specific wavelengths of light. Consequently, the wavelengths of light absorbed and emitted by a particular element are identical, leading to the emission and absorption spectra having lines at the same wavelengths. These spectral lines serve as a unique fingerprint for each element's presence in various samples. Gustav Kirchhoff and Robert Bunsen's discovery emphasized that the line emission spectrum of an element exactly matches its line absorption spectrum, forming the basis for spectroscopy.