Why can sound waves not be transverse in air?
(a) The density of air is too small to support transverse oscillations of its molecules.
(b) Air does not provide a restoring (shear) force for sideways displacement of its molecules.
(c) Gravity quickly pulls back any up–down motion of air molecules, so transverse waves cannot persist.
(d) Transverse mechanical waves can propagate only in one-dimensional media like stretched strings, not in three-dimensional gases.