Question

The presence of F-centres in a crystal makes it ______.

Options

• conducting

• colourless

• non-conducting

• coloured

Answer 1

The presence of F-centres in a crystal makes it coloured.

Explanation:

F-centres (Farbe centres) are anion vacancies in a crystal that trap free electrons. These trapped electrons can absorb certain wavelengths of visible light and re-emit the rest, giving the crystal a characteristic colour. For example, NaCl appears yellow when it contains F-centres.