Which of the following types is included in the leftmost group of the periodic table?

Base metals

The correct answer is option 4. Base metals.

The leftmost group of the periodic table is Group 1, which consists of alkali metals. Therefore, the correct option is not provided in the choices. However, if we consider the closest option, it would be Base metals.

It's worth noting that alkali metals are not usually referred to as "base metals," but rather as alkali metals. "Base metals" typically refers to certain common metals, including copper, lead, zinc, and others, but these are found in different groups of the periodic table.