12. the second period at the bottom of the table is called the

Elements in group 17 are known as “salt formers”. They are called halogens. ... The elements at the bottom of the table were pulled out to keep the table from becoming too long. The first period at the bottom is called the lanthanides. The second period at the bottom of the table is called the actinides.

Explanation:

The table itself is comprised of 7 periods and 18 groups, with the latest known ... here, 57, is located at the bottom of the table in the row called the Lanthanides.