In the activity where unripe tomatoes are bagged with a ripe banana, the tomatoes ripen because the banana releases:

1. A ripening banana continues to produce ethylene, a gaseous hormone. 2. Trapped in the bag, this ethylene reaches the unripe tomatoes. 3. Ethylene promotes fruit ripening, so the bagged tomatoes ripen. 4. Tomatoes bagged alone stay unripe, confirming the banana's ethylene is the cause and not abscisic acid, gibberellin or cytokinin. 5. Ethylene is the only one of the options that is a gas naturally released by ripening fruit. 6. So the result confirms ethylene as the gaseous ripening signal among the four options. _Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 16 Plant and Animal Hormones "Abscisic Acid - Activity", p.239_