For atoms in the periodic table, the given mass number is the sum of the number of the protons (also called the atomic number) and the number of the neutrons inside its nucleus. Mathematically,
mass number = atomic number + number of neutrons
Substituting,
39 = 19 + n
n = 39 - 19 = 20
Therefore, the answer is not found in the choices.
The answer is D) Velocity
Answer:
We have learned that refraction occurs as light passes across the boundary between two media. Refraction is merely one of several possible boundary behaviors by which a light wave could behave when it encounters a new medium or an obstacle in its path.
