To solve this problem, we need to identify which of the given options is an example of a colonial alga.$\newline$Let's analyze each option:$\newline \bullet$Volvox:$\newline$ - Volvox is a genus of green algae that forms spherical colonies.$\newline$ - Each colony consists of numerous individual cells embedded in a gelatinous matrix.$\newline$ - The cells are connected by cytoplasmic strands, allowing for coordinated movement and function.$\newline$ - Therefore, Volvox is a classic example of a colonial alga.$\newline \bullet$Ulothrix:$\newline$ - Ulothrix is a genus of filamentous green algae.$\newline$ - It forms unbranched filaments and is not considered colonial.$\newline \bullet$Spirogyra:$\newline$ - Spirogyra is another genus of filamentous green algae.$\newline$ - It is known for its spiral chloroplasts but does not form colonies.$\newline \bullet$Chlorella:$\newline$ - Chlorella is a genus of single-celled green algae.$\newline$ - It exists as individual cells and is not colonial.$\newline$Based on the analysis, the correct answer is Option 1: Volvox, as it is the only example of a colonial alga among the options provided.