Which of the following elements is a d-block element?

Step 1: Analyze the question We need to find which element belongs to the d-block of the periodic table. An element's block is decided by the sub-shell that receives its last (highest-energy) electron.

Step 2: Concept

• s-block: Groups 1 and 2 (last electron enters an s orbital)
• p-block: Groups 13 to 18 (last electron enters a p orbital)
• d-block: transition elements (last electron enters a 3d, 4d, or 5d orbital)
• f-block: lanthanides and actinides

Step 3: Check each option

• A. Calcium (Z = 20): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². The last electron enters 4s, so it is s-block (Group 2).
• B. Iron (Z = 26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶. The last electron enters 3d, so it is d-block, a transition metal.
• C. Lithium (Z = 3): 1s² 2s¹. The last electron enters 2s, so it is s-block (Group 1).
• D. Silicon (Z = 14): 1s² 2s² 2p⁶ 3s² 3p². The last electron enters 3p, so it is p-block (Group 14).

Step 4: Answer Only iron has its outermost-added electrons filling a d sub-shell, so the correct answer is B. Iron.

Exam tip: Remember the first-row transition metals in order: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Any element from this list (or in the central block of the periodic table) is d-block. Iron, copper, and zinc are the ones WASSCE and JAMB ask about most often.