Final answer:
The three-carbon alkyl group described is known as an isopropyl group, which features a branching chain at the middle carbon atom.
Step-by-step explanation:
The name for the three-carbon alkyl group CH3‑CH|‑CH3 is an isopropyl group. In organic chemistry, isopropyl denotes a branched-chain structure, specifically the middle carbon is bonded to the additional group or atom, in this case a methyl group (CH3). This structural feature distinguishes it from a straight-chain propyl group.