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Formaldehyde has the formula $\ce{CH2O}$, and the ratio of atoms in a simple carb is $\ce{1C:2H:1O}$. This fits the formula of formaldehyde. When I researched this, I found some sources saying that formaldehyde is the simplest carb, but other sources saying it is glycolaldehyde ($\ce{C2H4O2}$). Is formaldehyde a carbohydrate?

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up vote 5 down vote accepted

According to iupac definition

‘carbohydrate’ includes monosaccharides, oligosaccharides and
polysaccharides as well as substances derived from monosaccharides by reduction of the carbonyl group (alditols), by oxidation of one or
more terminal groups to carboxylic acids, or by replacement of one or more hydroxy group(s) by a hydrogen atom, an amino group, a thiol
group or similar heteroatomic groups. It also includes derivatives of these compounds....

But accoriding to wikibooks

the term is generally understood in the biochemistry sense, which
excludes compounds with only one or two carbons. Natural saccharides
are generally built of simple carbohydrates called monosaccharides
with general formula $\ce{(CH2O)n}$ where n is three or more...

Because formaldehyde and Glycolaldehyde(not a true sugar) has one and two carbon respectively in its strutures we can exclude both as a carbohydrate

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