Structural Organisation in Animals

Cockroach: the respiratory system consists of a network of tracheae that open to the outside through 10 pairs of small holes called spiracles, present on the lateral side of the body.
Of these, 2 pairs are on the thorax and 8 pairs are on the abdomen. So this description is true.
Rat: the right kidney is slightly higher (more anterior) in position than the left one, so the statement given is wrong.
Earthworm: the correct sequence of the alimentary canal is buccal cavity, pharynx, oesophagus, gizzard, stomach and intestine. The gizzard comes before the stomach, so the given sequence is wrong.
Frog: the body is divisible into head and trunk only; the neck and tail are absent.
So the true description is that of the cockroach with 10 pairs of spiracles.

Earthworms have no hard skeleton.
Their body cavity is a true coelom, filled with coelomic fluid and divided into compartments by septa.
The coelomic fluid is incompressible. When the circular and longitudinal muscles of the body wall contract against it, the fluid pressure makes the body segments stiff and turgid.
During burrowing the anterior end becomes turgid in this way and can be pushed into the soil; the fluid thus acts as a hydraulic (hydrostatic) skeleton.
Setae only provide a grip on the soil during locomotion, gut peristalsis moves food, and blood flows in a closed system of vessels; none of these gives turgidity to the body.
So the hydraulic skeleton is due to the coelomic fluid.