UPSC CDS II 2025 GK Paper

Concept:Transition metals are defined by partially filled d-orbitals in their $(n-1)$ shell, giving the general configuration $(n-1)d^{1-10}ns^{0-2}$.Explanation:Step 1: Transition elements occupy the d-block (groups 3 to 12). Their defining feature is the filling of $(n-1)d$ orbitals. Step 2: The outermost $ns$ orbital may have 0, 1, or 2 electrons. Thus the correct general form is $(n-1)d^{1-10}ns^{0-2}$. Step 3: Option A: $(n-2)d^{1-10}ns^{2}$ describes inner transition elements (f-block), not transition metals.Option B: $(n-2)f^{1-14}(n-1)d^{0-1}ns^{2}$ is for f-block elements.Option C: $ns^{2}np^{6}nd^{1-10}$ includes fully filled $np^6$, which is not the ground state of transition metals.Thus only option D matches the actual electronic configuration of transition metals.Answer:Option D: $(n-1)d^{1-10}ns^{0-2}$