Question about carbohydrate rings and enthalpy

There was a question in TBR:

The difference in the enthalpies of combustion for xylose (an aldopentose) and ribose (an aldopentose) can best be attributed to:

The Answer was steric repulsion in the furanose ring.

I have some questions regarding their answer explanation.

First, I can't remember, but are the main carbohydrate sugars (glucose, galactose, ribose, fructose) generally more stable in the ring form or straight chain form?


In their explanation, they say, "The repulsion...

Question about carbohydrate rings and enthalpy