Anomalous Behavior of Oxygen:- Like the usual trend of P-block elements, oxygen, the first member of gp. 16 differ from rest of the members of this group. The anomalous behavior of oxygen is due to the following properties:-
(i)          Small size.
(ii)         High electronegativity.
(iii)        Non-availability of d-orbitals in the valency shell.
Points of difference
(i)          Oxygen is a diatomic gas while others are complex solids.
(ii)         Oxygen is highly non-metallic due to high value of electronegativity.
(iii)        Oxygen is O2-ion very easily; the di-negative anions of other members are less common.
(iv)       Oxygen exhibits an oxidation state of -2 only except in OF2 where it has +2 state and peroxides where it has         1 state whereas rest all members show +4 and +6 oxidation states in addition to +2 oxidation state.
(v)         Oxygen molecule is highly stable because the two atoms are held together by fairly strong multiple bond having bond energy quite high. Thus ordinary oxygen is not active under ordinary conditions.
(vi)       Oxygen molecule is paramagnetic in nature in gaseous, liquid and solid states and has two unpaired electrons. Rest all are diamagnetic.
(vii)      Hydrogen bonding is present in water and may other compounds of oxygen due to high electronegativity of oxygen.
(viii)     Oxygen is the most abundant element on this planet.
(ix)       Oxygen is capable of forming P?-P? bonds with other elements of smaller size like carbon, nitrogen etc. the other members of this group do not show the tendency to exhibit such multiple bonding.
						

							Oxygen shows anomalous behaviour due to formation of p(pi)-p(pi) bond....2:-small size,high electronegativity,absence of d orbital in valence shell...3:-oxygen is second most electronegative element..4:-they show -2,+2,+4.+6 oxidation states5:-these elements reacts with acids,non metals,metals and form hydride6:-the well known universally used hydride of oxygen is water...
						

							oxygen is diatomic gas while other elements are polyatomic solidsh2o is liquid h2s&h2se are gaso2does not show higher oxidation state due to the absence of d-orbitals other elements show higher oxidation stateit is less reactive due to presence of double bond but other elements are more reactive due to presence of single bond
						

							
Oxygen has -2 oxidation state ,while all the other elements have +4 &+6 oxidation state.
But oxygen too have some exception in oxidation no. As in F2O oxygen has +2 oxidation state 
And in hydrogen peroxide H2O2 it having +1 oxidation state.