2. which of the following is unique for any given element?
a its mass number
b the number of its neutrons
c its atomic number

C its atomic number

Explanation:

Every element has a unique atomic number. The atomic number is always the same for a given element and does not change.

The number of protons in an atom is the atomic number. Protons are located in the nucleus. Being nuclei particles, they do not have a variable number. Their number is fixed and we can easily identify an atom with the number of protons, which is the atomic number.

chemists can use the electron cloud model to assign electrons to different atomic orbitals. atomic orbitals also explain the patterns in the periodic table

explanation:

i don't see a text, but i am gonna assume this *orbit* the curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the sun.