What is meant by a chain reaction?

A chain reaction refers to a sequence of reactions where a product of one reaction initiates further reactions. This is a crucial concept in chemistry, particularly in nuclear chemistry and some kinds of organic reactions. In this process, the products formed can trigger additional reactions, leading to an ongoing series of reactions that can exponentially increase in speed and magnitude.

For instance, in a nuclear chain reaction, the fission of one atom can release neutrons that go on to cause the fission of other atoms, creating more neutrons and perpetuating the process. This self-sustaining nature of chain reactions can lead to significant results, particularly in contexts such as nuclear reactors or explosions.

The other choices do not accurately describe a chain reaction. A linear sequence of reactions with no feedback does not encompass the self-sustaining nature intrinsic to chain reactions. A reaction that occurs in a straight line does not reflect the concept at all, as chain reactions can occur in various pathways and are not linear. Finally, a process that only requires one initial reactant does not capture the essence of a chain reaction, which often involves multiple products that contribute to subsequent reactions.