Which statement about the d-block elements of Period 4 of the periodic table is correct?
A chromium atom (Cr\text{Cr}Cr) in its ground state has the electron configuration 1s22s22p63s23p63d44s21\text{s}^2 2\text{s}^2 2\text{p}^6 3\text{s}^2 3\text{p}^6 3\text{d}^4 4\text{s}^21s22s22p63s23p63d44s2.
A titanium(III) ion, Ti3+\text{Ti}^{3+}Ti3+, contains exactly 2 unpaired electrons in its 3d3\text{d}3d sub-shell.
A copper(II) ion, Cu2+\text{Cu}^{2+}Cu2+, has the electron configuration 1s22s22p63s23p63d91\text{s}^2 2\text{s}^2 2\text{p}^6 3\text{s}^2 3\text{p}^6 3\text{d}^91s22s22p63s23p63d9.
Zinc and scandium are classified as transition metals because they belong to the d-block of Period 4.
