Learn French: Ce chocolat est croquant. - This chocolate is crunchy.

You would use the indefinite pronoun quelques-uns because chocolat is a masculine noun. The sentence would become Quelques-uns sont croquants.

Does the adjective croquant come from a verb?

Yes, it comes from the verb croquer, which means to crunch or to bite into. Croquant is literally the "crunching" form (the present participle), but it is commonly used as a standard adjective meaning crunchy or crisp.

Why is it ce chocolat instead of cet chocolat?

Ce is the standard masculine singular word for this or that. You only use cet when a masculine noun starts with a vowel or a mute H (like cet arbre or cet homme). Because chocolat starts with a consonant, it takes ce.

Do I pronounce the final "t" in croquant?

No, the final "t" is silent in the masculine form. However, if you were describing something feminine like an apple (une pomme), the adjective adds an "e" to become croquante, and then you do clearly pronounce the "t" sound.