How many neutrons are in the following isotope?
3818Ar
56
O
18
20
38

There are 20 neutrons in the isotope

Explanation:

In isotope , 18 represents atomic number and 38 represents mass number.

Atomic number : It is defined as the number of electrons or number of protons present in a neutral atom.

Thus, number of protons = atomic number = 18

Mass number is the number of the entities present in the nucleus which is the equal to the sum of the number of protons and electrons.

Mass number = Number of protons + Number of neutrons  = 38

Thus : 38 = 18 + Number of neutrons

Number of neutrons = 20

Thus there are 20 neutrons in the isotope

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