Answer: a positive standard reduction potential (E° of Cu 2+ /Cu).
- A a very high hydration enthalpy and atomisation energy
- B a positive standard reduction potential (E° of Cu<sup>2+</sup>/Cu)
- C a completely filled 4s orbital
- D no unpaired electrons
Correct answer: B. a positive standard reduction potential (E° of Cu<sup>2+</sup>/Cu)
Explanation: The high sum of its enthalpies of atomisation and ionisation is not balanced by hydration, giving Cu a positive E°(Cu<sup>2+</sup>/Cu). So it is not oxidised by H<sup>+</sup> of dilute acids.
Aqueous solutions of transition metal ions show characteristic colours caused by electrons absorbing visible light to jump between split d-orbitals; the exact colour depends on the metal, its oxidation state, and surrounding ligands.
Concept context
Transition metals (d-block) and lanthanides/actinides (f-block). Known for coloured compounds, variable oxidation states, complex formation, and catalytic properties. Frequently tested in JEE and NEET.