Final answer:
The claim that groups of stars formed from interstellar clouds leave the main sequence simultaneously is false; star masses determine the rate at which they evolve and leave the main sequence.
Step-by-step explanation:
The statement that interstellar clouds usually form groups of stars that leave the main sequence at the same time is false. When a cluster of stars forms from an interstellar cloud, it is true that they all form at roughly the same time from the same material and initially have similar compositions. However, these stars will have different masses, and due to this, they will go through their life cycles at different rates. The mass of a star determines its position and lifespan on the main sequence. More massive stars will leave the main sequence much faster than their lower mass counterparts. Therefore, within a group of stars formed together, some will leave the main sequence before others, leading to a spread in evolutionary stages.