Which of the following statements is correct about ionization energy? It

Analyze the question: We need the correct statement about ionization energy, which is the energy required to remove one mole of electrons from one mole of gaseous atoms, forming a positive ion (cation).

Concept: Ionization energy trends in the Periodic Table:

• Across a period (left to right): it generally increases, because nuclear charge increases while the electrons are added to the same shell. The nucleus holds the outer electrons more tightly and atomic radius decreases.
• Down a group: it decreases, because atomic radius increases, there are more inner shells shielding the outer electron, and the outer electron is held less tightly and is easier to remove.

Evaluating each option:

• A. Decreases across the periods: Wrong. It generally increases across a period.
• B. Results in the formation of an anion: Wrong. Losing electrons forms a cation (positive ion). Gaining electrons forms an anion.
• C. Causes metallic nuclei to disintegrate: Wrong. Ionization removes outer electrons only, and the nucleus is unaffected. Nuclear disintegration is radioactivity.
• D. Decreases down the group: Correct. For example, in Group 1: Li (520 kJ/mol) > Na (496) > K (419), so the energy needed falls as you go down.

Tip: Remember "Across → Up, Down → Down" for ionization energy: it goes up across a period and down a group. Also remember that ionization makes a cation (think "caTion = posiTive"), so you can eliminate option B quickly.