In a given column of the periodic table the elements have . a. similar properties
b. sequential atomic numbers
c. similar atomic masses
d. the same densities

a. similar properties

Explanation:

In a given column of the periodic table, the elements have similar properties.

A column on the periodic table is known as a group or family. The group is a vertical arrangement of elements  on the periodic table.

Elements in the same group have the same number of valence electrons after their group number.

For example, all the elements in group 1 have one valence electron. Those in group 2 have 2 valence electrons.

The valence electrons of an atom determines its chemical properties. So, all elements in the same group have the same chemical properties.

the answer is na (sodium)