What is the measurement of absorption of solar energy per unit area?

The measurement of absorption of solar energy per unit area is defined as energy flux. This term describes the rate at which energy is transferred through a given surface area and is commonly expressed in units like watts per square meter (W/m²). Energy flux takes into account not only the amount of solar energy hitting a particular area but also how effectively that energy is absorbed or transmitted by the surface in question.

Intensity, while closely related, often refers to the power carried by a wave per unit area in a direction perpendicular to that area, and may not specifically pertain to the absorption of energy. The term "density" typically refers to mass per unit volume and does not relate to the absorption of solar energy directly. "Magnitude" is a more general term that can refer to the size or extent of something and does not specifically indicate energy absorption.

Thus, energy flux accurately captures the concept of measuring how much solar energy is absorbed per unit area, making it the correct answer.