Classify the following substances into ionic, covalent, molecular or metallic :
MgO, `SO_2 , I_2, H_2O` (ice) , `SiO_2` (quartz), brass.

Explanation

To classify the given substances into ionic, covalent, molecular, or metallic, we will analyze each substance based on their bonding characteristics.

### Step-by-Step Solution:

1. **MgO (Magnesium Oxide)**:
- **Classification**: Ionic
- **Explanation**: MgO is formed from the transfer of electrons from magnesium (Mg) to oxygen (O), resulting in the formation of Mg²⁺ and O²⁻ ions. The electrostatic attraction between these oppositely charged ions constitutes ionic bonding.

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