The lightest transition element among the options provided is B) Sc (Scandium).
To understand why, it’s important to look at the atomic numbers of each element:
- A) Titanium (Ti) has an atomic number of 22.
- B) Scandium (Sc) has an atomic number of 21.
- C) Iron (Fe) has an atomic number of 26.
- D) Mercury (Hg) has an atomic number of 80.
As you can see, Scandium, with its atomic number of 21, is the lowest among the given elements, making it the lightest transition element here. Transition metals are those that have partially filled d orbitals and are located in groups 3-12 of the periodic table. While Scandium is often technically classified as a transition metal, it is at the very beginning of this group, hence it is the lightest one in the context of your options.