Which of the following possesses a poison sting and belongs to the class $Chondrichthyes$?

Pharyngeal gill slits are found in

Which fins are paired in fishes?

Which of the following statements are not true about shark?
$a$. The skin is tough and covered with placoid scales
$b$. They possess a swim bladder which regulates buoyancy
$c$. The tail of shark is heterocercal
$d$. Ampulla of Lorenzini present in the snout of shark is a thermoreceptor.
$e$. It has five pairs of gill slits covered by operculum

Which of the following characteristic features always holds true for the corresponding group of animals?

Choose the correct option with regards to $Chondrichthyes$.