Which type of waves can propagate in solids?

$Assertion :$ 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.

What are called waves? Mention their importance.

Transverse waves can propagate in

The figure shows wave fronts in still water moving in the direction of the arrow towards the interface $PQ$ between a shallow region and a deep (denser) region. Which of the lines shown may represent one of the wave fronts in the deep region?

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