What is the relative formula mass of ethene (C₂H₄)?

The correct option is 28.05.

The correct option is 28.05. 28.05 is correct because it directly supports the approved learning objective to represent alkene molecules in displayed, structural and molecular formula forms. This belongs to Structure and formulae of alkenes within Reactions of alkenes and alcohols (chemistry only), so the answer must use the correct organic chemistry context. The other options are incorrect when they confuse the organic family, formula type, reaction condition, product, or property being tested. Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.