Question

which one is least basic
NF3
NCl3
NBr3
NI3

Answer 1

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.

Answer 2

$NF_3$ is the least basic.

• Lewis basicity of any species is defined as the electron-donating tendency of that species.
• Among halogens, F is the most electronegative element.
• Due to high electron negativity, F attracts the lone pairs of nitrogen strongly. So, the lone pairs of electrons in the nitrogen atom are no longer available for donation.
• So, that's why among the trihalides of nitrogen $NF_3$ is the least basic.