What characterizes a scalar quantity?

A scalar quantity is defined by having magnitude only, without any associated direction. This means that a scalar can be completely described by a single value along with the appropriate unit of measurement. For example, concepts such as temperature, mass, and speed are scalar quantities.

The other characteristics mentioned in the options relate to vector quantities, which do have both magnitude and direction (like velocity or force). While scalars can change with time, that characteristic alone does not define them; rather, it is their lack of direction in their definition that distinctly sets them apart. Thus, option B captures the defining feature of scalar quantities accurately.