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. ( also put the options too)
