How can an element be identified using its line-emission spectrum?

An element can be identified using its line-emission spectrum because each element emits light at specific wavelengths when electrons transition between energy levels. These wavelengths correspond to particular colors and create a unique pattern of lines that is characteristic of that element, known as its emission spectrum. By comparing the observed wavelengths in the spectrum of an unknown sample with the known spectral lines of various elements, one can identify the element present in the sample. This method is highly effective because no two elements have the same emission spectrum, thus allowing for precise identification based on the analysis of these spectral lines.