Question

which one of the following is a main - group element?
cu
co
ce
cs
none of the above

Explanation:

Main - group elements are elements in groups 1 - 2 and 13 - 18 of the periodic table.

• Cu (Copper) is a transition metal (group 11).
• Co (Cobalt) is a transition metal (group 9).
• Ce (Cerium) is a lanthanide (a type of inner - transition metal).
• Cs (Cesium) is in group 1 (alkali metals, a main - group).

Answer:

Cs