Draw a lewis structure for hnc and assign the non-zero formal charges to each atom. draw the lewis structures with the formal charges minimized.

H-C-N H-N-C C-H-N Notice that C-H-N is the same as N-H-C just written backwards. ( i.e. they have the same connectivtiy.) You can exclude the last one with H in the middle since H has two bonds and 4 electrons around it. At this point you couldn't differentiate between the first two, so I would give you the connectivity in such a problem, which in this case is H-C-N.