Which of the following reactions will not occur? Give reasons.
`MgSO_4(aq)+Fe(s)to FeSO_4(aq)+Mg(s)`
(ii) `MgSO_4(aq)+Cu(s) to CuSO_4(aq)+Mg(s)`
(iii) `CuSO_4(aq)+Fe(s) to FeSO_4(aq)+Cu(s)`

Explanation

To determine which of the given reactions will not occur, we need to consider the reactivity series of metals. The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals higher in the series can displace metals lower in the series from their compounds in solution.

### Step-by-Step Solution:

1. **Identify the Reactivity Series**:
- The common reactivity series from most reactive to least reactive is: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminum (Al), Zinc (Zn), Iron (Fe), Lead (Pb), Copper (Cu), Silver (Ag), Gold (Au).
- From this series, we can see that Magnesium (Mg) is more reactive than Iron (Fe) and Copper (Cu).

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