What is a psychrometric chart used for?

A psychrometric chart is specifically designed to illustrate the relationships between various thermodynamic properties of moist air. It provides a graphical representation of properties such as temperature, humidity ratio, enthalpy, and specific volume. Engineers and HVAC professionals utilize the chart to analyze air conditions and determine how changes in temperature and moisture content affect air properties.

This tool is essential for designing heating, ventilation, and air conditioning (HVAC) systems, as it allows practitioners to evaluate how processes like cooling, heating, dehumidification, and humidification change the state of the air. Thus, finding properties of air under varying conditions is the primary purpose of a psychrometric chart, making it the correct choice for this question.