I’m confused how to do this

B. P (Phosphorus)

Explanation:

The element is be phosphorus.

This is true because phosphorus has a larger atomic radius than carbon. If you move than the group, elements gain additional electron shell. That additional electron shell keeps electrons far from the nucleus of the atom. This actually increases the atomic radius. Also, phosphorus is more electronegative than aluminum because phosphorus itself is a non-metal and non-metals are generally electronegative while aluminum is a metal and electropositive.  

Phosphorus has a lower ionization energy than argon because the ionization energy across the period (i.e from left to right) increases and across period 3, you will find phosphorus first before argon in the periodic table.

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.