- (1) Sm stands for Samarium, which is a rare earth element. Rare earth elements are a group of 17 elements that include the 15 lanthanides plus scandium (Sc) and yttrium (Y). Samarium $(\mathrm{Sm})$ is a member of the lanthanide series and is considered a rare earth element.
- (2) Hg stands for Mercury, which is a transition metal, not a rare earth element.
- (3) Zn stands for Zinc, which is a transition metal, not a rare earth element.
- (4) W stands for Tungsten, which is a transition metal, not a rare earth element.