During which type of cross is the inheritance of a single trait observed?

The correct response is the monohybrid cross because it specifically focuses on the inheritance of a single trait. In a monohybrid cross, an organism that is homozygous for one trait (for example, flower color) is crossed with an organism that is homozygous for another variant of that trait (for instance, purple flowers cross with white flowers). This allows observation of how that one trait is inherited through generations, following Mendel's laws of segregation.

In contrast, a trihybrid cross involves three traits, a dihybrid cross examines the inheritance patterns of two traits, and a polyhybrid cross takes into account more than two traits. These other types of crosses become increasingly complex and analyze the interactions and inheritance of multiple traits simultaneously, making them unsuitable for studying the inheritance of a single trait specifically.