Ans.
All vertebrates are chordates, but not all chordates are vertebrates. Both vertebrates and chordates show presence of pharyngeal gill slits, a nerve cord, and a post-anall tail in some stages of their life. However, all vertebrates have a vertebral column, developed from notochord present in embryonic stage, while vertebral column is absent in some chordates.
Thus, the correct answer is option). 'All vertebrates are chordates.'