Twenty different statistics students are randomly selected. for each of them, their body temperature (degreesc) is measured and their head circumference (cm) is measured. if it is found that requals0, does that indicate that there is no association between these two variables?

Yes.

Explanation:

r is a measurement of value of the linear correlation coefficient which represents all sample data as paired. If the value of r is estimated to be 0, this means that between body temperature (degrees C) and a head circumference (cm) exist no correlation. In statistics, dependence or correlation can be any relationship between two variables, even if it is not causal. It can be any statistical association.