hydrogen can form one covalent bond, oxygen can two , nitrogen can form four covalent bond out of which one is coordinate bond and carbon can form four covalent bonds
If we are talking about one single carbon atom, then 4 hydrogen atoms can be bonded to a carbon atom, because there is 4 electrons in the valence shell, and a valence shell needs 8 electrons in total, which causes the carbon to have 4 open bonds. A hydrogen has only one electron in its valence shell of 2, and needs one more to complete it. So, each hydrogen connects to 1 of 4 bonds on the carbon to complete the valence electron. Fun fact, CH4 is methane.
