In terms of atomic structure, explain why the first-ionization energy K is less than that of Ca.

The atomic structure indicates the number of protons, neutrons, and electrons in an atom.

In the atomic structure, the protons and the neutrons are positioned at the center of the nucleus while the electrons are located at the outer region of the atom.

The ionization energy is the amount of needed to eliminate a single electron from the outermost shell of an atom or a molecule.

Factors affecting the ionization energy includes:

On the periodic table, Potassium (K) is the 19th element and Calcium is the 20th element.

Postassium is located on Group 1 and period 4 while Calcium is located on the Group 2 and period 4 on the periodic table.

Now, as we move from left - right on the periodic table across the period, the ionization energy increases from left to right as a result of the size of the atom.

Here, the size of the atom of Calcium(Ca) is larger by a single electron compared to the size of Potassium(K).

Also, the positive nuclear charge on Calcium(Ca) is greater than that of Potassium(K) because from left - right on the periodic table, the nuclear charge increases,thereby increasing attraction of the outermost electron, thus more energy is needed to remove an electron.

Thus, since Calcium(Ca) tends to have a larger size of atom and a greater +ve nuclear charge than Potassium(K), then:

The first ionization energy of K will be lesser than that of Ca.

Therefore, from the above explanation, we can conclude that we've understood why the first-ionization energy K is less than that of Ca.

Learn more about atomic structure here:

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Potassium has less ionization energy because it does not take much energy to remove its single outer electron. Most elements want to have a complete outer shell, so since it has a lone electron in its outer shell, it will easily give up the electron to become more stable.

i'm assuming that the correct answer is indeed the first one/ "a"..