What is the composition of an isotope of calcium (atomic number 20)?

The correct answer to the question is: 20 protons, 25 neutrons, 20 electrons

The atomic number of an element is simply defined as the number of protons in the nucleus of the atom of the element. This simply implies that:

From the question given above,

Atomic number = 20

Therefore,

Since no two elements have the same atomic number (i.e proton number), we can conclude that the correct answer to the question is 20 protons, 25 neutrons, 20 electrons because the atomic number (i.e proton number) of calcium can not change

All other options have proton number that is not 20.

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The answer to your question is: last option.

20 protons

20 electrons

25 neutrons

Explanation:

Data

Calcium, atomic number 20

Atomic number indicates the number of protons in an element, so, if Calcium's atomic number is 20, it means that it has 20 protons.

In a neutral element, the number of protons = number of electrons, then

Calcium has 20 electrons.

Only the number of neutrons could change.

According to the previous description, the last option is correct.