What is meant by a chain reaction?

A chain reaction is defined as a sequence of reactions in which one of the products leads to further reactions, often resulting in a rapid and exponential increase in the number of products formed. This is particularly common in nuclear reactions or certain chemical reactions where the product created can induce additional reactions to occur.

By contrast, the other options do not accurately capture the essence of what a chain reaction entails. A linear sequence of reactions without feedback does not demonstrate the self-perpetuating nature characteristic of chain reactions. A reaction occurring in a straight line does not provide insight into the interconnectivity of reactions that typify a chain reaction. Additionally, suggesting that a process only requires one initial reactant does not address the crucial aspect of product-induced reactions facilitating further processes within a chain reaction. Thus, the definition that describes a sequence of reactions where a product causes more reactions is the most accurate interpretation of a chain reaction.