Unsaturated fatty acids are characterized by the presence of:

Unsaturated fatty acids are specifically defined by the presence of double bonds between carbon atoms in their hydrocarbon chains. This structural feature differentiates them from saturated fatty acids, which contain only single bonds. The presence of one or more double bonds introduces kinks in the fatty acid chain, affecting its physical properties and behavior, such as lowering the melting point and making it more fluid at room temperature.

Double bonds can be categorized as either cis or trans, influencing the molecule's shape and biological activity. In plant oils and fish oils, for example, the majority of fats are unsaturated, making them healthier dietary choices compared to saturated fats, which are typically solid at room temperature.

In the context of the other options, single bonds refer to the structure of saturated fatty acids, while triple bonds are characteristic of certain specific compounds, not general fatty acids. Covalent bonds broadly describe the types of bonds between atoms in molecules and do not specifically address the unique structure of unsaturated fatty acids. Therefore, the defining characteristic of unsaturated fatty acids is indeed the presence of double bonds.