Solution: Hormone which helps in the closing of stomata is abscisic acid.
Explanation:
- Efflux of water and potassium ion and halt in efflux of hydrogen ion result into closing of stomata.
- The influx of calcium ion also leads to closure of the stomatal pore.
- The halt in efflux of hydrogen builds up alkaline environment.
- The abscisic acid induces efflux of potassium that in turn initiates closure of stomata.