Find the number of metals which are commercially reduced by self-reduction from the given metals :
`Fe, Al, Z, Sn, Pb, Hg, Cu`.

Explanation

To determine the number of metals that can be commercially reduced by self-reduction from the given list of metals (Fe, Al, Z, Sn, Pb, Hg, Cu), we will follow these steps:

### Step 1: Identify the metals in the list
The metals provided are:
- Fe (Iron)
- Al (Aluminum)
- Z (Zinc)
- Sn (Tin)
- Pb (Lead)
- Hg (Mercury)
- Cu (Copper)

### Step 2: Determine the electropositivity of the metals
Self-reduction is typically applicable to less electropositive metals. The electropositivity of the metals in the list can be ranked as follows (from more electropositive to less electropositive):
1. Al (most electropositive)
2. Zn
3. Fe
4. Sn
5. Pb
6. Cu
7. Hg (least electropositive)

### Step 3: Identify the less electropositive metals suitable for self-reduction
From the ranking, the less electropositive metals are:
- Pb (Lead)
- Hg (Mercury)
- Cu (Copper)

### Step 4: Confirm the self-reduction process
Self-reduction is a process where a metal can be reduced from its ore without the need for an external reducing agent. The relevant ores for these metals are often sulfide ores:
- For Copper (Cu): Cuprous sulfide (Cu2S) can be partially oxidized to cuprous oxide (Cu2O) and then reduced to copper.
- For Lead (Pb): Lead sulfide (PbS) can also undergo a similar process.
- For Mercury (Hg): Mercury sulfide (HgS) can be reduced to mercury.

### Step 5: Count the metals that can undergo self-reduction
From the analysis, we find that the metals that can be commercially reduced by self-reduction are:
- Lead (Pb)
- Mercury (Hg)
- Copper (Cu)

Thus, the total number of metals that can be commercially reduced by self-reduction is **3**.

### Final Answer
The number of metals which are commercially reduced by self-reduction from the given metals is **3**.

---