order the elements Mg, K, Ca, S according to second ionization energy

I know that K would have the highest second ionization energy, then come S bec it takes more energy to remove an electron from a nonmetal than a metal, which is next ?

Your first two choices are correct.

Removing the second electron from both Mg and Ca is relatively easy because it is a single s electron in an outer shell, but Ca+ will be easier to ionize because the electron is farther from the nucleus than it is for Mg+.

To order the elements Mg, K, Ca, and S according to their second ionization energies, we need to understand the general trend in ionization energy across the periodic table.

Ionization energy is the energy required to remove an electron from a neutral atom or ion. In general, ionization energy increases as you move from left to right across a period and decreases as you move down a group in the periodic table.

Let's analyze the four elements you mentioned:

1. Magnesium (Mg) is a metal located in Group 2 of the periodic table. It has a relatively low second ionization energy compared to the other elements in the list. This is because after the first electron is removed, the positive charge of the ion increases, making it easier to remove the second electron.

2. Potassium (K) is also a metal but is located in Group 1, which means it has a higher second ionization energy than magnesium. After the first electron is removed, the ion becomes positively charged, making it more difficult to remove the second electron.

3. Calcium (Ca) is another metal in Group 2. Similar to magnesium, it has a lower second ionization energy compared to potassium. However, since it is placed after potassium in the list, it has a higher second ionization energy than potassium.

4. Sulfur (S) is a nonmetal located in Group 16 of the periodic table. Nonmetals generally have high ionization energies compared to metals. This means sulfur will have the highest second ionization energy among the elements mentioned.

Therefore, the correct order of the elements from lowest to highest second ionization energy is: Mg, Ca, K, S.