Which of the following statements is true of fatty acids?
a. All fatty acids have the same chain length.
b. All fatty acids are solid at room temperature.
c. The more carbon atoms and nitrogen atoms present in a fatty acid, the shorter the fatty acid is.
d. The more hydrogen atoms attached to carbon atoms, the more saturated a fatty acid is.
e. All fatty acids have only double bonds.
The correct answer and explanation is :
Correct Answer: d. The more hydrogen atoms attached to carbon atoms, the more saturated a fatty acid is.
Explanation:
Fatty acids are long hydrocarbon chains that contain a carboxylic acid group (-COOH) at one end. They are classified based on the presence and number of double bonds between carbon atoms in their hydrocarbon chain.
Saturated fatty acids have no double bonds between carbon atoms. This means that all carbon atoms (except the carboxyl carbon) are fully “saturated” with hydrogen atoms. The more hydrogen atoms present (i.e., the fewer double bonds), the more saturated the fatty acid is. Therefore, statement (d) is correct: the more hydrogen atoms a fatty acid has, the more saturated it is.
Now, let’s break down why the other choices are incorrect:
- (a) All fatty acids have the same chain length: This is false. Fatty acids can vary widely in chain length, typically ranging from 4 to over 24 carbon atoms. Chain length affects properties like melting point and solubility.
- (b) All fatty acids are solid at room temperature: Not true. Saturated fatty acids (like those in animal fat) are usually solid at room temperature, but unsaturated fatty acids (common in plants and fish oils) are often liquid due to the kinks in their structure caused by double bonds.
- (c) The more carbon atoms and nitrogen atoms present in a fatty acid, the shorter the fatty acid is: This is contradictory. More carbon atoms make a fatty acid longer, not shorter. Also, typical fatty acids do not contain nitrogen; nitrogen is more commonly found in amino acids and other compounds.
- (e) All fatty acids have only double bonds: This describes polyunsaturated fatty acids, not all fatty acids. Saturated fatty acids have no double bonds, and monounsaturated ones have just one.