AFCT English Complete Practice Test Guide

The term "soluble" specifically refers to a substance's ability to dissolve in a liquid, typically water. When a substance is described as soluble, it means that when it is mixed with a solvent (like water), it breaks down into individual molecules or ions that become integrated into the liquid. This process results in a homogeneous solution, where the original substance is no longer visible as a separate entity.

The other options do not accurately capture the meaning of "soluble." While some substances may indeed produce heat when dissolved, this is not a characteristic of solubility itself. "Remains unchanged" contradicts the idea of dissolving, as a soluble substance transforms when it dissolves. The toxicity of a substance is unrelated to its solubility; a substance can be soluble and non-toxic or insoluble and toxic. Thus, the correct understanding of "soluble" is clearly indicated by the ability to dissolve in a liquid.