Final answer:
Magnesium is used in flares and flashbulbs because it produces a bright, white flame ideal for visibility and illumination. Other elements burn with different colors due to their emission spectra.
Step-by-step explanation:
The metallic element often used in flares and flashbulbs because it burns with a bright, white light is magnesium. Magnesium is a choice for this purpose because when it burns, it produces a light with nearly every frequency, resulting in a brilliant white flame. This white light is highly desirable for flares and flash photography for visibility and illumination purposes. In contrast, other elements burn with different colored flames, which are not as versatile for these applications.
For instance, sodium imparts a bright yellow color to a flame, whereas other alkali metals such as lithium produce a bright crimson color, and the heavier alkaline earth metals like calcium and strontium produce various shades of red. These various colors are a part of the emission spectrum of these elements, which is visible when they are energized by heating or an electrical discharge.