Chiral Centers in Fructose

Steps:

• A chiral center is a tetrahedral carbon atom bonded to four different substituent groups.
• Fructose is a ketohexose with open-chain formula CH2OH-C=O-(CHOH)3-CH2OH.
• Carbons 1 and 6 are CH2OH groups, symmetric and non-chiral; carbon 2 is the carbonyl, trigonal planar and non-chiral.
• Carbons 3, 4, and 5 each bond to H, OH, and two distinct carbon chains, making them chiral.

Why B is correct:

• X and Y correspond to two of carbons 3–5, which meet the four-different-substituents criterion for chirality.

Why the others are wrong:

• A includes Z, which is likely carbon 1, 2, or 6 and lacks four different groups.
• C names only Y, ignoring the other chiral carbon X.
• D names only Z, which is non-chiral.

Final answer: B