The reagent ‘X’ is

A substance known as a dehydrating agent dries or eliminates water from a material. The responding molecule loses a water molecule in chemical processes where dehydration takes place.
Ethene is the end product of heating ethanol with too much concentrated sulfuric acid at a temperature of 170°C. The concentrated acid is recovered unaltered and merely serves as a dehydrating agent. 

Hence, the correct option is option (C)  95% H₂SO₄ at 170^oC.