Answer : The correct option is,
![Mg(OH)_2\rightarrow Mg^(2+)+2OH^-](https://img.qammunity.org/2019/formulas/chemistry/high-school/p6u1ge51sfd2vuf3yuzbd5u0rq5uq0nvlq.png)
Explanation :
Ionization : It is a type of process in which the molecule obtain a negative and a positive charge by losing or gaining the electrons.
(1)
![Mg(OH)_2\rightarrow Mg^(2+)+2OH^-](https://img.qammunity.org/2019/formulas/chemistry/high-school/p6u1ge51sfd2vuf3yuzbd5u0rq5uq0nvlq.png)
This reaction is an example of ionization in which the magnesium hydroxide ionizes into magnesium (2+) ion and hydroxide ion.
(2)
![C+O_2\rightarrow CO_2](https://img.qammunity.org/2019/formulas/chemistry/high-school/zgsczz5dal92j8x6l7gom5ddwcxp13re9v.png)
This reaction is not an example of ionization reaction. This reaction is an example of synthesis reaction in which the two or more reactants that are present in their elemental state combine to give a new product.
(3)
![H_2CO_3\rightarrow H_2O+CO_2](https://img.qammunity.org/2019/formulas/chemistry/high-school/wr9r6zhhbixkhrw4lc8n9qxnlzcmo935pn.png)
This reaction is not an example of ionization reaction. This reaction is an example of decomposition reaction in which the larger reactant molecule decomposes to give two or more smaller products.
(4)
![SO_2+H_2O\rightarrow HSO_3^-+H^+](https://img.qammunity.org/2019/formulas/chemistry/high-school/9lm4mzr09dtarphhj5vney00c6q5eoukf8.png)
This reaction is not an example of ionization reaction.
Hence, the correct option is,
![Mg(OH)_2\rightarrow Mg^(2+)+2OH^-](https://img.qammunity.org/2019/formulas/chemistry/high-school/p6u1ge51sfd2vuf3yuzbd5u0rq5uq0nvlq.png)