H3COH. How do you know which is the central atom ?
According to Valence Shell Electron Pair Repulsion theory(VSEPR), the central atom of a compound or molecule will be that atom which is most elcetropostive compare to other aroms of that particular compound or molecule.
Now,in case of H3COH, hydrogen atom is most electropositive but as it has only one valence elcetron it cant be served as central atom.
Again ,between C and O ,the carbon atom is more electropositive than oxygen so carbon atom acts as a central atom.The carbon atom has four valency while oxygen atom has two valency.