The correct answer is C. Mercury vapour and argon.
Fluorescent tubes are filled with a mixture of mercury vapor and argon gas. When an electric current is passed through the tube, the mercury vapor is excited and emits ultraviolet light. This ultraviolet light then strikes the phosphor coating on the inside of the tube, causing it to fluoresce, or emit visible light.
Sodium oxide and neon are not commonly used in fluorescent tubes. Sodium oxide is a white solid that is used in some types of sodium vapor lamps. Neon
is a colorless gas that is used in neon signs. Mercury oxide is a black solid that is used in some types of mercury vapor lamps.Argon is a colorless, odorless, and tasteless gas that is used in many different types of lamps, including fluorescent tubes. It is a noble gas, which means that it is very stable and does not react with other elements. Argon helps to prevent the mercury vapor in a fluorescent tube from breaking down and also helps to improve the efficiency of the tube.