Reinecke's salt is named ammonium diamminetetrakis(thiocyanato-$\kappa N$)chromate(III). Its formula is

The anion has Cr(III), two neutral NH3 and four NCS-, so its charge is $+3+0-4=-1$. One $\mathrm{NH}{}_4{}^{+}$ balances it, and the coordination number is 6. Other options change the ligand counts or the cation number.