Order of Formulae for Ethene and Alkenes

Steps:

• Define empirical formula as simplest whole-number ratio of atoms in a compound.
• Identify ethene's molecular formula as C2H4, the actual number of atoms.
• Determine empirical formula for C2H4 as CH2 by dividing subscripts by 2.
• Recall general formula for alkene homologous series as CnH2n.

Why A is correct:

• A sequences empirical (CH2 for ethene), molecular (C2H4 for ethene), and general (CnH2n for series), matching definitions.

Why the others are wrong:

• B incorrectly places general formula before molecular, mixing series with ethene-specific.
• C starts with general, which applies to the series, not ethene alone.
• D leads with molecular, skipping empirical as the simplest ratio.

Final answer: A