Final answer:
Thallium (Tl) is an example of a main-group metal element in period number 6 of the periodic table, specifically within group 13.
Step-by-step explanation:
A main-group metal element in period 6 of the periodic table would be a member of either group 1, group 2, or groups 13-18. To find a main-group metal in period 6 specifically, we look at period 6 of the periodic table and identify the metals that fall under these groups.
Considering groups, group 1 contains alkali metals, which are highly reactive, and group 2 contains alkaline earth metals, which are also quite reactive, but not as much as the alkali metals. Groups 13-18 contain a variety of metals, metalloids, and nonmetals. However, not all elements in these groups are metals, particularly in period 6 as it contains a mix of metals, metalloids, and nonmetals.
For instance, group 13 starts with the metal Boron but includes a main-group metal element in period 6, Thallium (Tl). Therefore, Thallium is an example of a period 6 main-group metal. It's important to remember, that the transition metals, while also located in period 6, do not fall into the main-group category.