Question

Why do some metals glow when burning in a flame?

Answer 1

The radiation that some metals emit falls inside the visual spectrum so we are able to see colours.

Explanation:

When faced with a burning flame, the electrons take energy to go to higher energy levels and emit radiation on their way back to lower energy levels.

Metals such as `"Na"`, `"Ca"`, `"Sr"`, `"Ba"`, `"Cu"` give out radiation with frequencies inside the visual spectrum. so we are able to see them.

But metals such as `"Mg"` emit radiation in the UV area and since human eye is not sensitive to UV radiation, we don't see any colour when a salt of `"Mg"` is faced with a burning flame.

Watch this video of the flame test - credits to this video's owner