Ella set up an experiment to investigate one of her questions. She set up one test tube to look like Figure 1. She set up another test tube similar to Figure 1 but without
a lamp, and placed it in a dark closet. A day later, Ella checked the water level in
each test tube.

What was the test (independent) variable in the student's experiment?
A. The amount of light.
B. The amount of time.
C. The water level in the test tube.
D. The amount of oxygen released.

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.