Answer:The formulas of ionic compounds are:
a)
![CuBr](https://img.qammunity.org/2020/formulas/chemistry/college/3m2pahqx34aet60eimpqsepbxs83x4y6oj.png)
b)
![Mn_2O_3](https://img.qammunity.org/2020/formulas/chemistry/college/pues8v34frgucozpwtg562mnsqx6arr6m5.png)
c)
![Hg_2I_2](https://img.qammunity.org/2020/formulas/chemistry/college/bv7x2j01p1i0y5332wv7qo7bnzs7udak1u.png)
d)
![Mg_3(PO_4)_2](https://img.qammunity.org/2020/formulas/biology/college/8uu5hicnvb3hl0jakqu1zhajyav97twxu0.png)
Step-by-step explanation:
Formulas for the an ionic compounds is determine by:
Criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of the other ions. This results in the formation of a neutral compound.
(a) Copper bromide :Given that it contains
ion.
![Cu^++Br^-\rightarrow CuBr](https://img.qammunity.org/2020/formulas/chemistry/college/wey5ir07u7nekauuds9slviwbdhzp8u7xt.png)
(b) Manganese oxide : Given that it contains
ion.
![Mn^(3+)+O^(2-)\rightarrow Mn_2O_3](https://img.qammunity.org/2020/formulas/chemistry/college/fajs2dqgcgdpo98m25wmz1tr2m0gzw0569.png)
(c)Mercury iodide :Given that it contains
![Hg_2^(2+)](https://img.qammunity.org/2020/formulas/chemistry/college/jdv17ma1gtniywcf8yli9qncmsgaf7jtsn.png)
![Hg_2^(2+)+I^-\rightarrow Hg_2I_2](https://img.qammunity.org/2020/formulas/chemistry/college/ggo704wf992vbo0cco75zcv8w5246e68sn.png)
(d) Magnesium phosphate :Given that it contains
![PO_4^(3-)](https://img.qammunity.org/2020/formulas/biology/college/6bml3k0v467vo15g58248demd6a2dzl31o.png)
![Mg^(2+)+PO_4^(3-)\rightarrow Mg_3(PO_4)_2](https://img.qammunity.org/2020/formulas/chemistry/college/bsln2rvwbmexrcu9a55jglu3jcvl20rr75.png)