Unsaturated and saturated lipids exhibit different characteristics based on their structures. which characteristic is unique to saturated fats?
forms covalent, carbon-to-carbon bonds
is a liquid at room temperature
contains the maximum number of hydrogen atoms
consists of fatty acids and a carboxyl group

The right answer is contains the maximum number of hydrogen atoms.  

A saturated fatty acid is a fatty acid having carbon atoms fully saturated with hydrogen (see figure). Each carbon carries as many hydrogens as possible. We can not add hydrogen to the molecule: it is saturated.

All the bonds between the carbons are simple (no carbon-carbon double bonds).

Saturated fats, a type of lipid, are triglycerides obtained by reacting three molecules of saturated fatty acids on a molecule of glycerol.

Contains maximum of hydrogen atoms.

The saturated fatty acid has only hydrogen bonds and unsaturated fatty acid is double or triple bonds.

The unique feature of saturated fatty acids is that it contains only hydrogen bonds. This means it has maximum number of hydrogen in it as compared to that of the unsaturated fatty acid.

Both consists fatty acids and carboxyl group and forms carbon-carbon bond.

The difference is hydrogen bond present in the saturated fats.