Ascientist has isolated a fatty acid that has 26 carbons bonded together. most of the carbon atoms in the chain are connected by single bonds, but there is a double bond between the number 9 and 10 carbons in the chain. the only other elements in the compound are hydrogen and oxygen. based on this information, the compound is a (an) fatty acid. saturated monounsaturated essential polyunsaturated

This is a monounsaturated fatty acid .
Saturated fatty acids are those where all the C atoms are bonded by single bonds.
When they are bonded by single bonds, each C has the maximum amount of H atoms it can bond to. It’s then saturated with H atoms.
When there are fatty acids with double bonds, then they are called unsaturated bonds as they don’t have the maximum number of H atoms.
The fatty acid in the question all the C atoms are bonded by single bonds except for one double bond , therefore it’s monounsaturated fatty acid

Neither model is able to show the reactivity of potassium.