The valence electrons of the substance's atoms feel an effective nuclear charge of +7. if the unknown substance has lower ionization energies than chlorine (cl), what other characteristics would you expect the substance to exhibit?

 1. B it has less ioni. energy, less likely to form ion and react, therefore its a halogen under Cl on the periodic table, and has a wider radius due to more shells 

2. B ionic bond = cation + anion, Mg has charge 2+ and Cl has charge 1- forming MgCl2 
also Mg is a metal and Cl is non metal 

but H and Cl ions also bond to form hydrogenchloride. but both H and Cl are non-metals. so B is the best answer.

It is 4.92 e-4 sorry if i am wrong