Which one of Na, Al and Fe will satisfy the following? Answer with justification.
`M_2 O_3`, is not affected by water.

Explanation

To determine which metal (Na, Al, or Fe) corresponds to the formula \( M_2O_3 \) and is not affected by water, we can follow these steps:

### Step 1: Identify the Oxide
The formula \( M_2O_3 \) indicates that the metal \( M \) has a valency of +3, as it combines with three oxygen atoms (each with a -2 charge). Therefore, the metal must be trivalent.

### Step 2: Analyze the Metals
- **Sodium (Na)**: Sodium typically forms \( Na_2O \), which corresponds to a +1 oxidation state. Therefore, sodium cannot be \( M \) in \( M_2O_3 \).
- **Aluminium (Al)**: Aluminium has an atomic number of 13 and commonly forms \( Al_2O_3 \), which corresponds to a +3 oxidation state. Thus, aluminium can be \( M \) in \( M_2O_3 \).
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