Which of the following is a simple respiratory organ?

$O_{2}$ exchange with $CO_{2}$ by simple diffusion over the entire body surface takes place in:
$I.$ Sponges
$II.$ Coelenterates
$III.$ Flatworms
Select the correct option to complete the given statement.

Choose the correct option by matching the organisms in Column-$I$ with their respective respiratory organs in Column-$II$.

Column-$I$	Column-$II$
$(p)$ Sponges	$(I)$ Through tracheal tubes
$(q)$ Insects	$(II)$ Through lungs
$(r)$ Molluscs	$(III)$ Vascularized gills
$(s)$ Reptiles	$(IV)$ Simple diffusion over their entire body surface
	$(V)$ By their moist cuticle

Find the correct sequence for $p-q-r-s$.

What is the site of gaseous exchange in an insect?

Given below are four matchings of an animal and its kind of respiratory organ:
$I.$ Silver fish - Trachea
$II.$ Scorpion - Book lung
$III.$ Sea squirt - Pharyngeal gills
$IV.$ Dolphin - Skin
The correct matchings are:

The skin is a respiratory organ in ...........