Answer
Aldohexose- 4 chiral carbons, 16 stereoisomers.
Ketohexose- 3 chiral carbons, eight stereoisomers.
Work Step by Step
-Aldohexose has 4 chiral carbons, so it forms $2^4 =16$ stereoisomers.
Ketohexose has 3 chiral carbons, so it forms $2^3 = 8$ stereoisomers.