In an experiment, the factor of interest is called the
a. control group
b. experimental group
c. hypothesis
d. variable

The correct answer is the (d.) variable. In an experiment, the factor of interest is called the variable. Variable is the one who is representing the materials or the things that being experimented. In this way, the scientists are able to determine or get track on what's happening on both sides.

The higher you go up the less oxygen there is 

The answer is c water is the solvent and salt is the solvent