Consider the diagram below to identify the gas X.
Gas X is
Hydrogen
Calcium reacts with water to form calcium oxide with the evolution of hydrogen gas.
Ca(s) + H2O(i) → CaO(s) + H2(g)
The gas evolved can be shown as hydrogen by bringing a burning candle near the mouth of the boiling tube, the gas catches fire and burns with a pop sound.
The correct answer is C.