Explanation:

- Heinrich Rudolph Hertz was a pioneering physicist who clarified and expanded the electromagnetic theory of light that was originally proposed by James Clerk Maxwell.

- Frequency is the correct attribute associated with Hertz. The unit of frequency, the hertz (Hz), is named after him. It measures the number of cycles per second of a periodic phenomenon.

- Heat, light, and sound, while each may involve frequencies in their own specific contexts, are not directly named after Hertz in terms of standard SI units.

- The unit for heat is typically calories or joules, for light it can be measured in lumens or candela, and sound's pressure level is measured in decibels.

- Understanding Hertz's contributions helps connect his work to the technological advancements in communication, such as radio waves.

Frequency is the correct answer.