The correct structures of trans-[NiBr₂(PPh₃)₂] and meridonial-[Co(NH₃)₃(NO₂)₃], respectively, are

Solution

Chemistry ma’am · 3 steps

Check what sits opposite: trans means Br faces Br, and mer means two NO₂ groups face each other.

1. Trans in square planar. In square planar [NiBr₂(PPh₃)₂], trans means the two Br lie on one straight line through Ni, and so do the two PPh₃. In these drawings, diagonally opposite corners of the X are trans to each other, and neighbouring corners are cis.
2. Fac or mer. For octahedral [Co(NH₃)₃(NO₂)₃], look at what sits opposite each NO₂. In fac, the three NO₂ cover one face, so every NO₂ is trans to an NH₃. In mer, the three NO₂ lie on a meridian, so two of them are trans to each other.

   Option	Ni complex	Co complex	Gives you
   (a)	Br opposite Br	every NO₂ opposite an NH₃	trans and fac
   (b)	each Br opposite a PPh₃	every NO₂ opposite an NH₃	cis and fac
   (c)	each Br opposite a PPh₃	two NO₂ opposite each other	cis and mer
   (d)	Br opposite Br	upper-right and lower-left NO₂ opposite each other	trans and mer

3. So. Only (d) has the two Br trans in the nickel complex and a meridional arrangement in the cobalt complex.

The idea to keep. To tell isomers apart in a drawing, find the trans partner of each ligand. In MA₃B₃, if two identical ligands are trans to each other it is mer. If each A is trans to a B, it is fac.

Answer from the NTA final answer key. Solution by PrepWiser.