Introduction to Biochemistry - Quiz 2.6.1

They contain multiple hydroxyl groups and they contains an aldehyde or ketone group.

Ribose and Glucose are monosaccharides.

Ketose must contain a ketone group, a ketone group is a C double bond O NOT at the end of the carbon chain, C is the only molecule with that structure.

$ C_1 $ has two hydrogens - that cannot be a chiral center
$ C_2 $ is $ sp^2$ hybridized - that cannot be a chiral center
$ C_4 $ has two hydrogen - that cannot be a chiral center

$ C_3 $ is a chiral center - its four bonds links to four different groups.

Fischer convention use (D) and (L) designations, it is done by drawing the carbohydrate with the aldehyde/ketone group on the top and then see if the lowest chiral carbon has hydroxyl group on left or right under the Fischer's projection. Note that this has nothing to do with the sugar's optical property. It is just a convention.

The lowest chiral carbon has hydroxyl group of the left, therefore it is a L sugar. It is an aldehyde, therefore the answer is L-idose.

I think this is the answer - but edx gives me a wrong answer - it thinks the middle OH bond is on the same plane. I just do not agree - I believe that middle carbon is $ sp^3 $ hybridized, so there is no way for 3 bonds to be on the same plane.