The floor of the fourth ventricle contains all except -
Nuclei in the floor of 4th ventricle

Abducent nucleus lies below facial colliculus.
Vestibular nuclei below vestibular area.
Dorsal nucleus of vagus below vagal triangle and hypoglossal nucleus below the hypoglossal triangle.

Option 'b' requires some explanation

The facial nerve is present on the floor of the 4th ventricle at facial colliculus. But the facial nucleus is not present in the floor of the 4th ventricle.
Abducent nucleus
Facial nucleus
Dorsal vagal nucleus
Hypoglossal nucleus