Concept:The inner coating of a fluorescent tube is a phosphor material that converts ultraviolet light into visible light.
Explanation:A fluorescent tube is a gas-discharge lamp containing mercury vapour.
When electricity passes through the tube, the mercury vapour produces intense ultraviolet radiation.
The inner wall of the tube is coated with a sulphide compound.
This coating absorbs the invisible ultraviolet rays and re-emits them as visible light.
Zinc sulphide (
ZnS) is a common phosphor that performs this function efficiently.
It gives a bright glow and remains stable under the operating conditions of the tube.
Therefore, zinc sulphide is the sulphide commonly used for coating electric fluorescent tubes.
Answer:C. Zinc sulphide (
ZnS)