Fructose is an example of:

Fructose has the molecular formula $$\text{C}_6\text{H}_{12}\text{O}_6$$, which means it is a six-carbon (hexose) sugar. Its open-chain structure contains a keto group ($$\text{C}=\text{O}$$) at the second carbon atom, rather than an aldehyde group at the first carbon.

Sugars are classified based on two criteria: the type of carbonyl group (aldose if aldehyde, ketose if ketone) and the number of carbon atoms (triose for 3, tetrose for 4, pentose for 5, hexose for 6, heptose for 7). Since fructose has a ketone group and six carbons, it is classified as a ketohexose.

An aldohexose would be a six-carbon sugar with an aldehyde group — glucose is an example. A pyranose refers to the six-membered ring form of a sugar, which is a structural form rather than a classification of the sugar itself. A heptose is a seven-carbon sugar, which fructose is not.

Therefore, fructose is an example of a ketohexose, and the correct answer is Option B.