Molecule is the general term used to describe any atoms that are connected by chemical bonds. Every combination of atoms is a molecule. A compound is a molecule made of atoms from different elements. All compounds are molecules, but not all molecules are compounds.
One example of a molecule is 
(chlorine).
Examples of a compound is NaCl (sodium chloride) or 
(water)
Answer:
2.17
Explanation:
To calculate pH using the hygrogen ion concentration we must use the following formula:
- log (H+) = pH
All we have to do now is plug in our hygrogen ion concentration and put it in our calculator.
- log (6.8 × 10⁻³) = 2.17
Don't forget proper figures for pH!
Normally, cortisol is present in the body at higher levels in the morning, and at it is lowest at night. Although stress isn’t the only reason that cortisol is secreted into the bloodstream, it has been termed “the stress hormone” because it’s also secreted in higher levels during the body’s stress response and is responsible for several stress-related changes in the body.
The correct answer is option C, that is, the universal law of gravitation.
According to Newton's law of universal gravitation, every particle fascinates every other particle in the universe with a force that is directly equivalent to the product of their masses and inversely proportional to the square of the distance between their centers. This is a usual physical law obtained from empirical observations by what Isaac Newton knew as inductive reasoning.
