Question

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

Explanation:

To determine the main - group element, we analyze each option:

• Cs (Cesium): It is in Group 1 (alkali metals) of the periodic table. Group 1 elements are main - group elements.
• Ce (Cerium): Cerium is a lanthanide element, which belongs to the inner - transition metals (f - block) and not to the main - group elements.
• Co (Cobalt): Cobalt is a transition metal (d - block) and not a main - group element.
• Cu (Copper): Copper is also a transition metal (d - block) and not a main - group element.

Since Cs is a main - group element, we can identify the correct option.

Answer:

A. Cs