Which of the following is an ionic compound?
O CO2
O H2O
O CH4
OKCI

the first one since it mean carbon oxide

Explanation:

and u need a cation and anion to create a compound which is what that is

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.