The diagram shows the displayed formula of a molecule of butane.

What is the empirical formula of butane?
CH2\mathrm{CH_{2}}CH2
CH3\mathrm{CH_{3}}CH3
C2H5\mathrm{C_{2}H_{5}}C2H5
C4H10\mathrm{C_{4}H_{10}}C4H10
102 exam-style questions on OCR GCSE Chemistry 2.1 Purity and separating mixtures, covering 2.1.1 Pure substances and melting point data, 2.1.2 Relative formula mass and empirical formula, 2.1.3 Formulations as useful mixtures, 2.1.4 Techniques for separating mixtures, and 2.1.5 Chromatography and Rf values. Each one has a worked solution and a mark scheme showing where the marks go.