How is the ripeness of apples determined?

Determining the ripeness of apples primarily relies on assessing their firmness and color. Firmness is a crucial indicator because ripe apples should feel solid but not overly hard; a certain level of give indicates that the fruit has matured properly. The color of the apple also plays a significant role, as different varieties of apples have specific color traits that signal when they are ripe. For instance, a change from green to yellow or the development of red hues can indicate readiness for harvest and consumption.

Other factors mentioned in the other choices, such as size and weight or shape and smell, can provide some indications about freshness and quality but are not as definitive for determining ripeness. Temperature and humidity are environmental factors that affect the growth of apples but do not directly indicate the ripeness of the fruit itself. Therefore, firmness and color remain the most reliable means of assessing an apple's ripeness.