Which of the following statement is not true for halogens
1)chlorine has highest electron gain enthalphy
2)all forms monobasic oxyacids
3)all but flourine shows positive oxidation states
4)all are oxidising agents
(3) All but fluorine show positive oxidation states.
Due to high electronegativity and small size, F forms only one oxoacid, HOF known as Fluoric (I) acid. Oxidation number of F is +1 in HOF.