Which region of the periodic table contains elements with a partially filled f sublevel?

• A. Lanthanides and actinides
• B. Alkali metals
• C. Halogens
• D. Transition metals

Answer: (A)

Verified step by step guidance

1. Recall that the periodic table is divided into blocks based on the electron sublevel that is being filled with electrons: s-block, p-block, d-block, and f-block.
2. Understand that the f-block elements are characterized by having electrons filling the f sublevel, which corresponds to the 4f and 5f orbitals.
3. Identify that the f-block elements are located in the two rows placed separately at the bottom of the periodic table, known as the Lanthanides (4f) and Actinides (5f).
4. Recognize that Alkali metals belong to the s-block, Halogens belong to the p-block, and Transition metals belong to the d-block, so none of these have partially filled f sublevels.
5. Conclude that the region containing elements with a partially filled f sublevel is the Lanthanides and Actinides.