1.) KI 2.)HCl 3.) MgS 4.) NO
Which compound has the least ionic character?
Degree of ionic character can be determined based on differences in electronegativity.
The smallest difference in your list of 4 would be between Nitorgen (N) and Oxygen (O), with a difference of 3.44 - 3.04 = 0.40 (all other pairs in your list have larger differences)
Answer: 4.) NO since N and O are both non metals, and have close electronegativities.