Identify the formula for each compound below: 
a) Potassium hexanitritocobaltate (III)
b) sodium tetrachloronickelate (II)
c) tetraamminechloridonitrito–N–cobalt (III) nitrate

• A. a) K₃[Co(NO₃)₆], b) NaNiCl, c) [Co₄(NH₃)(NO₂)Cl]NO₃
• B. a) K[Co(NO₂)₆], b) Na₂Ni₄Cl, c) [Co(NH₃)₄(NO₃)Cl]NO₂
• C. a) K₃[Co₆(NO₂)], b) NaNiCl₄, c) [Co(NH₃)(NO₂)Cl]NO₃
• D. a) K₃[Co(NO₂)₆], b) Na₂NiCl₄, c) [Co(NH₃)₄(NO₂)Cl]NO₃

Answer: (D)