Final answer:
Sucrose is not readily synthesized from formaldehyde in simulations of early Earth conditions due to its complex disaccharide structure which requires biological enzymatic processes not present in these simulations.
Step-by-step explanation:
The sugar that is not readily made from formaldehyde in experiments simulating conditions on primitive Earth is sucrose. Formaldehyde oligomerization under prebiotic conditions can lead to a variety of simple sugars, but sucrose is not typically one of them due to its complex disaccharide structure comprising α-D-glucopyranose and β-D-fructofuranose linked through an α-1→2 glycosidic bond.
As such, sucrose is a non-reducing sugar which means it does not have free aldehyde or ketone groups available to react with formaldehyde. Instead, sucrose is commonly formed in plants such as sugar cane and sugar beets through biological enzymatic processes that are not replicated in early Earth simulating experiments.