This unit on the gaseous state is one of 10 first year units produced by the Independent Learning Project for Advanced Chemistry (ILPAC). The unit consists of two levels. Level one deals with the distinctive characteristics of gases, then considers the gas laws, in particular the ideal gas equation and its applications. Level two concentrates on the kinetic theory of gases, deviations from ideal behavior, and the distribution of molecular velocities in a gas. The necessary calculations and their solutions are stressed throughout the unit. Three experiments, exercises (with answers), and pre- and post-tests are included. Additional exercises and a discussion of the liquefaction of gases are provided in appendices. Students completing this ILPAC unit assume a greater responsibility for their own learning and can work, to some extent, at their own pace. By providing guidance, and detailed solutions to exercises in the units, supported by the optional use of video-cassettes, the project allows students to study A-level chemistry with less teacher contact time than a conventional course demands. (JN)