Answer:
5. 4; 3; 2
Step-by-step explanation:
Carbon is in group 4, so it has 4 valence electrons and needs 4 electrons to be stable (octet rule). So it may share 4 electrons by a single, double or triple bond, then the maximum atoms it can be bond is 4.
Nitrogen is in group 5, so it has 5 valence electrons and needs 3 electrons to be stable. So it may share 3 electrons by a single, a double or a triple bond, then the maximum atoms it can be bond is 3.
Oxygen is in group 6, so it has 6 valence electrons and needs 2 electrons to be stable. So it may share 2 electrons by a single or a double bond, then the maximum atoms it can be bond is 2.