Why would an atom with high electronegativity be a great match for an atom with low ionization energy?

Because the easier a metal donates an electron (Low Ionization Energy), the more readily a non-metal with high electromagnetically will accept it.  

Thus they match well, - one readily donates, the other readily accepts. This is how ionic bonding occurs.  

Hope this helps.

the correct answer would be b) volume versus temperature, because they are also directly proportional.