The element with electron configuration 1s$^2$ 2s$^2$ 2p$^6$ 3s$^2$ 3p$^1$ belongs to

Step 1: Analyze the question We are given the configuration 1s² 2s² 2p⁶ 3s² 3p¹ and must find its block, period and group.

Step 2: Key concepts

• Block: determined by the subshell that receives the last electron (s, p, d or f).
• Period: equals the highest principal quantum number (the outermost shell).
• Group (older Nigerian syllabus): equals the number of valence electrons for the main groups.

Step 3: Solve

• The last electron enters the 3p subshell, so the element is in the p-block.
• The highest shell is n = 3, so it is in period 3.
• The valence electrons are 3s² 3p¹, which gives 2 + 1 = 3 electrons, so it is in group 3 (group 13 in the modern IUPAC numbering).
• The total number of electrons is 2 + 2 + 6 + 2 + 1 = 13, so the element is aluminium (Al).

Step 4: Check the options

• A: s-block, group 1. Wrong, because the last electron is in a p orbital.
• B: p-block, group 2. The block is right but the group is wrong, since there are 3 valence electrons.
• C: s-block, group 3. The block is wrong.
• D: p-block, period 3, group 3. Correct.

Tip: To place an element quickly, look at the last subshell filled (it gives the block), the biggest number in front (the period), and add up the electrons in the outermost shell (the group). Aluminium is always p-block, period 3, group 3 (13).