Which of the following is least basic?A NI3 b NBr3c NCl3d NF3 Please explain

Dear Sneha

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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Arun (askIITians forum expert)

Sir sorry to object ur ans. I am presenting my ans. Below as per my opinion think on it plz. I think NF3 is more basic than NI3. REASON: Basicity is the ability to donate lone pairs of electrons. But when it comes to comparing it we should look at how easily lone pair can be donated. In case of NI3 iodine atom has vacant d orbital so it will accept lone pair from Nitrogen atom to form back bond. But in case of NF3, Fluorine do not have any vacant orbital therefore here lone pair on nitrogen atom is more free to donate since it is not participating in back bonding. So NF3 is more basic than NI3 which means NI3 is less basic than NF3. 2) Also Basicity decreases down the group in the periodic table.As N is same in all compounds we must look at the ligands bonded to the central atom and I has atomic no. Greater than F and thus it will comes in 5th period while F is in 2nd period.SO THE LEAST BASIC IN THE ABOVE ORDER IS NI3.I hope it will help youRegards ROHIT.