The cause of sweet taste in fruits is :

The correct answer is D) Fructose. Fructose is a ketohexose (C6H12O6) and is the sweetest of the common natural sugars. It occurs free in fruits and honey, and it is the main reason ripe fruit tastes sweet. Fruits also contain glucose and sucrose, but fructose contributes most of the sweetness.

• Maltose (A): A disaccharide of two glucose units, formed when starch breaks down, as in germinating grain and malt. It is mildly sweet and is not the main sugar of fruits.
• Ribose (B): A pentose sugar (C5H10O5) that forms the backbone of RNA and ATP. It is not the primary sugar stored in fruit.
• Lactose (C): The sugar of milk, made of glucose and galactose. It is much less sweet and is absent from fruits.

Core concept: carbohydrate chemistry and the sugar profile of plant foods. For Mains, this links to the diet and nutrition debate on fruit juices versus whole fruit, free sugar intake, and the health effects of high-fructose products.

Trap: Aspirants often pick sucrose or glucose because they are the sugars they know best. Sucrose is the table sugar and is not the single answer here; the question asks for the specific sugar behind fruit sweetness.