Transition metals exhibit characteristic d-block properties

Steps:

• Locate vanadium (group 5), chromium (group 6), and cobalt (group 9) in the d-block of the Periodic Table, classifying them as transition metals.
• Transition metals have partially filled d orbitals, enabling variable oxidation states through d-electron involvement in bonding.
• Incomplete d subshells allow d-d electron transitions, absorbing visible light and forming colored compounds.
• Strong metallic bonding from delocalized d electrons results in high melting points for these elements.

Why A is correct:

• Transition metals, by definition, display all three properties due to their d-block electron configuration (ns¹⁻² (n-1)d¹⁻¹⁰).

Why the others are wrong:

• B omits high melting points, a key feature of d-block metallic bonding.
• C excludes colored compounds, arising from d-d transitions.
• D ignores variable oxidation states, central to transition metal reactivity.

Final answer: A