NI3 Is least basic as because of larger size of iodine the tendency to donate electron is less due to less availability of electrons around the central metal atom.
NF3 is least basic because F is most electronegative and it will attarct the lone pair of N atom and thus the electrons will the less available form donation. As the size of hailde ion increases the electronegativity of halide ion decreases and the basic charater of NX3 increases.
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Avian Blaze answered this
well NI3 is definitely the most basic..
nf3<ncl3<nbr3<ni3
in ncl3 there are chances of backbonding which reduces the basicity
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Ranjeet Kumar answered this
NF3 cause of more electronegativity of F
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Ashmita Debnath answered this
NF3 should have been the least basic due to it's electronegativity. But it is not the case because Chlorine has a vacant d-orbital, which forms a back bond with nitrogen, and thus traps electrons.
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pratikprakash0240... answered this
Ni3 because I HAS VACANT d-orbital , but fluorine does not have vacant orbital ,so it can't hold lone pair of nitrogen