Which element counts as a transition element?
- Amelting point $98\,^\circ\text{C}$; density at r.t.p. $1.0\,\text{g cm}^{-3}$; colour of oxide at r.t.p.: white
- Bmelting point $328\,^\circ\text{C}$; density at r.t.p. $11.3\,\text{g cm}^{-3}$; colour of oxide at r.t.p.: yellow
- Cmelting point $651\,^\circ\text{C}$; density at r.t.p. $1.7\,\text{g cm}^{-3}$; colour of oxide at r.t.p.: white
- Dmelting point $1907\,^\circ\text{C}$; density at r.t.p. $7.2\,\text{g cm}^{-3}$; colour of oxide at r.t.p.: green