Which of the carbanions shown is the most stable? (The hydrocarbon shown is the parent of one of them.)

The hydrocarbon shown is propene; loss of a proton from its methyl group gives the allyl anion, whose negative charge is delocalised over two terminal carbons by resonance. The ethyl, n-propyl and isopropyl anions are localised sp${}^3$ carbanions, and alkyl groups destabilise a carbanion through their electron-donating effect, so the allyl anion is the most stable.