What are the terms that describe these values for the element oxygen?

18 = Mass umber

8 = atomic number

Explanation:

An atom is smallest unit of a matter or substance.It consist of three subatomic particles : electrons, protons, neutrons.

Protons and neutrons are located in the center of an atom where while mass of an atom is concentrated.

Mass number = Number of protons + Number of neutrons

Atomic number = Number of protons = Number of electrons (for a neutral atom)

General representation of an element is given as:

where,

Z represents Atomic number

A represents Mass number  

X represents the symbol of an element

Oxygen is the 8th element of the periodic table and is written as , thus 8 = atomic number and 18= Mass number

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explanation: