Transition metal properties for elements 21–30

Steps:

• Proton number 21–30 corresponds to first-row transition metals (Sc to Zn) with incomplete d subshells.
• Identify statements matching transition metal traits: variable oxidation states and colored compounds.
• Statement 3 indicates colored compounds due to d-d electron transitions.
• Statement 4 indicates variable oxidation states from d-electron involvement.

Why D is correct:

• Statements 3 and 4 align with the definition of transition metals (IUPAC: elements with incomplete d subshell, enabling variable valency and color in compounds).

Why the others are wrong:

• A: Statements 1 and 2 lack specificity to d-block properties; 1 may fit s-block, 2 fits p-block gases.
• B: Statement 1 is too broad (many elements show +2 state); 4 is correct but paired wrongly.
• C: Statement 2 unrelated (gases are not in 21–30); 3 is correct but paired wrongly.

Final answer: D