Which of the following is false? Sound waves are _________ waves.

Sound is a mechanical wave: it needs a medium (solid, liquid or gas) to travel. In air it travels as a longitudinal wave of compressions and rarefactions, i.e. a pressure wave. So 'pressure', 'longitudinal' and 'mechanical' are all correct descriptions. Sound is not electromagnetic; electromagnetic waves such as light can travel through a vacuum, but sound cannot. So 'electromagnetic' is the false statement.