Sodium, a highly reactive element, appears silvery-white in its metallic form. When sodium is heated, it emits a bright yellow flame, which is the most characteristic color associated with the element. This yellow flame is due to the sodium atom's electronic transitions, where electrons in the outer shell absorb energy and then release it as light at a specific wavelength, resulting in the yellow color.

The color of sodium can be further explained by its electronic configuration. Sodium has an atomic number of 11, with an electron configuration of 1s² 2s² 2p⁶ 3s¹. When sodium is heated, the outermost electron in the 3s orbital is excited to a higher energy level. As this electron returns to its ground state, it releases energy in the form of light. The specific wavelength of light emitted corresponds to the yellow color, which is visible to the human eye.

According to the National Institute of Standards and Technology (NIST), the peak emission wavelength of sodium vapor is approximately 589.0 nm, which falls within the yellow region of the visible spectrum. This information is supported by various scientific studies and experiments conducted over the years.

In addition to its yellow flame, sodium also exhibits other colors under different conditions. For example, when sodium is dissolved in water, it forms a solution that appears yellow due to the presence of sodium ions. This is because the sodium ions absorb certain wavelengths of light, resulting in the observed color.

In summary, sodium is silvery-white in its metallic form and emits a bright yellow flame when heated. This yellow color is a result of electronic transitions within the sodium atom, which release energy in the form of light at a specific wavelength. The peak emission wavelength of sodium vapor is approximately 589.0 nm, corresponding to the yellow region of the visible spectrum.