To determine how many electrons are in a [tex]\(Ca^{2+}\)[/tex] ion, we need to start by understanding the electronic structure of a neutral calcium atom.
1. Determine the neutral state:
- Calcium (Ca) is an element with an atomic number of 20. This means that a neutral calcium atom has 20 protons in its nucleus and, in its neutral state, it also has 20 electrons.
2. Understand the ionization:
- The notation [tex]\(Ca^{2+}\)[/tex] indicates that the calcium ion has lost 2 electrons. The [tex]\(2+\)[/tex] charge shows that there are two more protons than electrons in the ion.
3. Calculate the remaining electrons:
- If the neutral calcium atom originally had 20 electrons and it loses 2 electrons to become [tex]\(Ca^{2+}\)[/tex], we subtract the lost electrons from the original count:
[tex]\[
20 \, \text{electrons} - 2 \, \text{electrons} = 18 \, \text{electrons}
\][/tex]
Thus, a [tex]\(Ca^{2+}\)[/tex] ion has 18 electrons.
The correct answer is:
B. 18
