Question

Which one of the following pairs of atomic numbers represents elements belonging to the same group?

• A. $11$ and $20$
• B. $13$ and $30$
• C. $13$ and $31$
• D. $14$ and $31$

Answer 1

The correct option is C $13$ and $31$

The elements with the same valence electrons belong to the same group. The pair of atomic numbers 13 and 31, represents elements belonging to the same group. They correspond to Al and Ga. They belong to group 13 or IIIA.