Figure: Displayed structures of two substances

Substance A is solid at room temperature and substance B is a gas. Which explanation is most appropriate?
A must contain ions that are free to move
A has larger molecules, so stronger intermolecular forces than B
B contains ionic bonds but A does not
B has stronger forces between its molecules than A
48 exam-style questions on Edexcel GCSE Chemistry 2.5 Types of substance, covering 2.5.1 Classifying substances by structure and bonding, 2.5.2 Properties of ionic and simple molecular substances, 2.5.3 Giant covalent structures: diamond and graphite, 2.5.4 Fullerenes, graphene and simple polymers, 2.5.5 Properties of metals and non-metals, and 2.5.6 Limitations of bonding models and representations. Each one has a worked solution and a mark scheme showing where the marks go.