the question says assume the valencies of hydrogen, nitrogen and carbon in the compounds are 1, 3 and 4 from this i must draw a structural formulae for hydrogen cyanide and cyanogen that are consistant with these valencies. please help

Question

H : C::: N:
Does that work?

thanks but does that not then give N the valence of 4 in stead of three

No. The valence electrons are shared with C in a triple bond.

Mark--Those two unpaired electrons on the right hand side of the N atom don't count as a valence.