To determine the symbol representing calcium atoms that have lost two electrons, let's follow these steps:
1. Identify the element and its standard atomic symbol:
- The element in question is calcium, which has the chemical symbol [tex]\( \text{Ca} \)[/tex].
2. Understand the change in electron configuration:
- Calcium atoms normally have 20 electrons. Losing electrons results in the formation of a positively charged ion (cation).
3. Determine the charge on the ion:
- When a calcium atom loses two electrons, it will have 18 electrons but still retains 20 protons in its nucleus.
- The number of protons (20) minus the number of electrons (18) results in a net positive charge of +2 ([tex]\(20 - 18 = +2\)[/tex]).
4. Write the correct ion symbol:
- The correct notation for an ion includes the element symbol and its net charge.
- For a calcium ion that has lost two electrons, the symbol will be [tex]\( \text{Ca}^{+2} \)[/tex].
In summary, the symbol representing calcium atoms that have lost two electrons is [tex]\( \text{Ca}^{+2} \)[/tex], which matches option 4.
So, the correct answer is:
[tex]\[ \boxed{Ca^{+2}} \][/tex]
