<span>You can answer this question by getting the atomic number and atomic mass of Oxygen from a periodic table. There you will find that the atomic number is 8, that means, by definition, that it has 8 protons. This is, because atomic number is defined as the number of protons of an element. Given that the atom is neutral, that implies that the atoms have the same number of electrons than protons. So you already know that the oxygen atoms has 8 protons and 8 electrons. The number of neutrons can vary, which is what defines the isotopes. Given that the atomic mass of oxygen is 15.999, that means that most atoms of oxygen has 8 neutrons (8 protons +8 neutrons = 16 atomic mass). But you can not be sure that a specific atom of oxygen has 8 neutrons, nevertheless, given that the other options are discarded (because they do not have 8 protons and 8 electrons), the only correct answer is the option A. 8 protons, 8 electrons, and 8 neutrons.</span>
The composition of an oxygen atom is A. 8 protons, 8 electrons, and 8 neutrons. This can be determined by using information from the Periodic Table: atomic number and the mass number. The atomic number gives the number of protons. This is also equal to the number of electrons. The difference of the mass number and the atomic number gives the number of neutrons.
<h3>FURTHER EXPLANATION</h3><h3>Subatomic Particles in an Atom</h3>
Atoms are made up of subatomic particles: protons, neutrons, and electrons.
Protons and neutrons are found in the nucleus or center of the atom. Protons are positively charged and neutrons are uncharged.
Electrons are found in electron orbitals around the nucleus.
<h3>Periodic Table of Elements</h3>
The number of protons, neutrons, and electrons an element has can be determined from the atomic number and the mass number of the element. These are information that can be found in the Periodic Table.
In the simplest Periodic Tables, two numbers are found in the square for each element: the atomic number which is the smaller number and the atomic mass which is either given as a whole number or as a decimal.
The atomic number tells the number of protons the element has. It gives the atom its identity.
In a neutral atom, the number of protons is equal to the number of electrons. Therefore, the atomic number also gives the number of electrons.
The atomic mass is the weighted average of the masses of the different forms of the element (or "isotope"). They usually are expressed in decimals. When this value is rounded off to a whole number, it can be indication of the total number of protons and neutrons in the atom. This is because the protons and the neutrons are the heavier subatomic particles and give the atom its mass. Hence, it is also called the mass number.
The mass number is the sum of the protons and the neutrons found in the nucleus of an atom.
<h3>Composition of an oxygen atom</h3>
Atomic Number = 8
Mass number = 16
number of protons = atomic number = 8
number of electrons = atomic number = 8
number of neutrons = (mass number - atomic number)
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