What are the characteristic of all chordates at some point during their life cycle?

Possession of notochord

Possession of dorsal hollow nerve chords.

Possession of pharyngeal gill-slits

Possession of  tail

Explanation:

All animals in the chordate group posses the following characteristics either throughout their entire life cycles or at some points in it:

Presence of notochord

Presence of dorsal hollow nerve chords.

Presence of pharyngeal gill-slits

Possession of  tail.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds