Heating ethanol with excess concentrated sulphuric acid produces:

The correct answer is ethene.Key Points

• Ethene is produced when ethanol is heated with excess concentrated sulphuric acid, which acts as a dehydrating agent.
• The reaction takes place through an elimination process, where a molecule of water is removed from the ethanol molecule, resulting in the formation of ethene.
• When pure, the gas has a little "sweet and musky" smell and is combustible.
• It is colorless.
• The simplest alkene is this one. 

Additional Information

• Ethanol is a primary alcohol with the molecular formula C₂H₅OH, commonly used as a fuel, solvent, and disinfectant.
• Concentrated sulphuric acid is a strong acid with the molecular formula H₂SO₄, commonly used in the chemical industry as a dehydrating agent, catalyst, and electrolyte.
• Ethyne (acetylene) is a two-carbon alkyne with the molecular formula C₂H₂, commonly used in the welding and cutting industry as a fuel gas.
• Butane is a four-carbon alkane with the molecular formula C₄H₁₀, commonly used as a fuel gas in lighters, stoves, and heaters.
• Ethane is a two-carbon alkane with the molecular formula C₂H_6, commonly used as a fuel gas and refrigerant.