Scientific must be supported by observations and results from many investigations and are not absolute.

theories

Explanation:

A scientific theory is a specific type of theory used in the scientific method.  A scientific theory is an unproven concept, it is a hypothesis. That is, a theory refers to a concept that needs to be explained and tested through a series of experiments. In other words, we can say that scientific theories must be supported by observations and results of many investigations and are not absolute.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)