The activation energy of an endothermic reaction

The fact that the total amount of energy in a system remains constant is a(n)

How are the terms group and period used on the periodic table

Scientists often have to deal with numbers that are either very large or very small. for example, the radius of the sun is approximately 696,000 kilometers, while bacterial cells are as small as 1.9 × 10-4 millimeters. express each number in an alternate form.