Dispersion can take place for

Are the waves propagating in solids transverse,longitudinal or both?

The angle between particle velocity and wave velocity in a transverse wave is

$Assertion :$ When a beetle moves along the sand within a few tens of centimeters of a sand scorpion,the scorpion immediately turns towards the beetle and dashes towards it.
$Reason :$ When a beetle disturbs the sand,it sends pulses along the sand's surface. One set of pulses is longitudinal while the other set is transverse.

The angle between the particle velocity and wave velocity in a transverse wave is [except when the particle passes through the mean position].

Transverse and longitudinal waves can propagate in solids,whereas only longitudinal waves can propagate in air. Explain this statement.