Fructose has multiple chiral centers, leading to the formation of 16 optical isomers. This can be calculated by the formula \( 2^n \), where \( n \) is the number of chiral centers. Fructose has 4 chiral centers, so the number of optical isomers is \( 2^4 = 16 \).
Step 2: Conclusion.
Thus, the correct answer is 16.