Which of the following facts is not truegt

Options

A. If `E^(@)(M^(n+)//M)` is negative, `H^(+)` will be reduced to `H_(2)` by the metal M
B. If `E^(@)(M^(n+)//M)` is positive `Mn^(2+)` will e reduced to M by `H_(2)`
C. In a cell `M^(n+)//M` electrode is attached to hydrogen-half cell. To produce spontaneous cell reaction, metal M will act as negative electrode.
D. Compounds of active metals `(Zn,Na,Mg)` are reducible by `H_(2)` whereas those of noble metals `(Cu,Ag,Au)` are not reducible.

Explanation

To determine which of the following statements is not true, we will analyze each statement based on the principles of electrochemistry.

### Step-by-Step Solution:

1. **Understanding Electrode Potentials**:
- The standard electrode potential (E0) indicates the tendency of a species to be reduced. A positive E0 means a strong tendency to gain electrons (be reduced), while a negative E0 indicates a tendency to lose electrons (be oxidized).

2. **Analyzing Statement 1**:
- Statement: "If E0 for this electrode is negative, H⁺ will be reduced to hydrogen by the metal M."
- Explanation: If E0 is negative, the metal M is a strong reducing agent and can reduce H⁺ to hydrogen. This statement is **true**.

3. **Analyzing Statement 2**:
- Statement: "If E0 for the electrode is positive, Mn²⁺ will be reduced to M by hydrogen."
- Explanation: A positive E0 indicates that Mn²⁺ is stable and can be reduced, while hydrogen (which has a lower E0) will be oxidized. Thus, this statement is **true**.

4. **Analyzing Statement 3**:
- Statement: "In a cell, electrons are attached to the hydrogen half-cell to produce a spontaneous cell reaction; metal M will act as the negative electrode."
- Explanation: For a spontaneous reaction, the metal M must act as the anode (negative electrode) where oxidation occurs. This statement is **true**.

5. **Analyzing Statement 4**:
- Statement: "Compounds of active metals (zinc, sodium, magnesium) are reducible by hydrogen, whereas those of noble metals are not reducible."
- Explanation: Active metals have a negative E0 and act as reducing agents, meaning they cannot be reduced by hydrogen. This statement is **not true** because active metals do not get reduced by hydrogen; instead, they can reduce other species.

### Conclusion:
The statement that is not true is: "Compounds of active metals (zinc, sodium, magnesium) are reducible by hydrogen, whereas those of noble metals are not reducible."

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