Properties of transition metals (Z=21-30)

Steps:

• Identify range: Proton number 21-30 corresponds to scandium to zinc, the first transition metal series.
• Recall key traits: These elements show variable oxidation states, form colored compounds, act as catalysts, and form complexes due to d-block electrons.
• Evaluate statements: Assume 3 involves variable oxidation states or catalysis; 4 involves colored compounds or complex formation, both indicative of transition metals.
• Eliminate others: Statements 1 and 2 likely describe general metal properties not unique to this range.

Why D is correct:

• Statements 3 and 4 align with d-block characteristics per periodic table trends, where incomplete d subshells enable these properties.

Why the others are wrong:

• A: Statements 1 and 2 lack specificity to transition metals, possibly applying to s- or p-block.
• B: Includes 1 (non-specific) with 4, but misses core indicator 3.
• C: Both 2 and 3 may not fully confirm the range without 4's supporting trait.

Final answer: D