In CO which element holds electron more tightly

Oxygen

Explanation:

The covalent bond is the chemical bond between atoms where electrons are shared, forming a molecule. Covalent bonds are established between non-metallic elements, such as hydrogen H, oxygen O and chlorine Cl. These elements have many electrons in their outermost level (valence electrons) and have a tendency to gain electrons to acquire the stability of the electronic structure of noble gas. The shared electron pair is common to the two atoms and holds them together.

If the atoms are different, as in this case, the bond will be polarized towards the most electronegative atom, because it will be the atom that attracts the pair of electrons with more force.

Oxygen has more electronegativity than carbon, so it will attract electrons shared with carbon more strongly.

O, better know as oxygen, has a higher ionization, causing it tot hold electrons more tightly.