Answer:
Mass number = 4
Atomic number = 2
Step-by-step explanation:
Mass numbers and atomic numbers are ways of identifying elements and explaining their properties.
Mass Number
The mass number describes the number of particles in the nucleus. This means that the mass number is the total number of protons plus neutrons. In the diagram above, the green particles are neutrons and the red particles are protons. There are 2 neutrons and 2 protons, so the mass number is 4.
Mass number is measured in amu. Amu stands for atomic mass units. Neutrons and protons both weigh 1 amu, so this atom weighs 4 amu.
Atomic Number
Atomic numbers are the most identifying part of any atom. Every element on the periodic table has a different atomic number. The atomic number is equal to the number of protons in an atom. We know that the red particles in the diagram are protons because they have a positive charge. There are 2 protons, so the atomic number must be 2.
Since we know the atomic number, we can identify the exact element. This diagram depicts helium, which always has 2 protons. Specifically, this is Helium-4 (elements can be written with their mass numbers hyphenated).