In which of the following molecules are all the bonds not equal? NF3,ClF3,BF3,AlF3

The correct answer is a.
In ClF3 all bonds are not equal due to trigonal-bipyramidal (sp^3d − hybridisation) geometry of ClF3 molecule.
BF3 and AlF3 show trigonal symmetric structure due to sp^3 – hybridization.
NF3 shows pyramidal geometry due to sp^3 hybridisation.

i think by bonds u mean bond lenghts
bond lenghts are equal when the bonds lie on the same plane,
of all...CLF3 has 4 lone pairs and 3 bond pairs.
as a result  the structure is pentagonal biplanar. and the bond lenghts are not equal since two bond pairs are located at axial pos. and hence at different plane