. Which element has the highest electronegativity
Electronegativity of an atom is defined as its tendency to attract a shared pair of electrons towards itself in a covalent bond.
The electronegativity increases on moving along the period from left to right and decreases on moving down the group from top to bottom.
Thus, the electronegativity of O will be the highest amongst the given options.
Hence, the correct option is C: O.