Answer: This because of Oxidation reaction of enzyme polyphenol oxidase presents in fruit cells with Oxygen when exposed to the air.
The oxidation reaction turns fruits brown.
Acidity lowers pH, and therefore affects or inhibits polyphenol oxidase.Therefore it activities slows down because low pH affects the 3D protein structure of enzyme.As a result the brownish effect is slowed down.
Refregeration aslo slows down activities of this enzyme,and therefore browniing
Step-by-step explanation: