How many of the following metals can be extracted by auto - reduction ?
`Fe, Zn, Pb, Al, Hg, Cu, K, Ca`

Answer

To determine how many of the given metals can be extracted by auto-reduction, we need to analyze the metals listed: Fe, Zn, Pb, Al, Hg, Cu, K, and Ca.

**Step 1: Understand Auto-reduction**
Auto-reduction is a process used primarily for extracting less electropositive metals from their sulfide ores. This process involves heating the sulfide ores in the presence of air, converting them into oxides, which then react with the remaining sulfide to produce the metal and sulfur dioxide gas.

**Step 2: Identify the Metals**
The metals listed are:
- Fe (Iron)
- Zn (Zinc)
- Pb (Lead)
- Al (Aluminum)
- Hg (Mercury)
- Cu (Copper)
- K (Potassium)
- Ca (Calcium)

**Step 3: Classify the Metals**
- Less Electropositive Metals: Cu (Copper), Pb (Lead), Hg (Mercury)
- More Electropositive Metals: Fe (Iron), Zn (Zinc), Al (Aluminum), K (Potassium), Ca (Calcium)

**Step 4: Determine Which Metals Can be Extracted by Auto-reduction**
From the classification:
- Copper (Cu) can be extracted by auto-reduction.
- Lead (Pb) can also be extracted by auto-reduction.
- Mercury (Hg) can be extracted by auto-reduction.

The other metals (Fe, Zn, Al, K, Ca) are more electropositive and cannot be extracted by auto-reduction.

**Step 5: Count the Metals**
The metals that can be extracted by auto-reduction are:
1. Copper (Cu)
2. Lead (Pb)
3. Mercury (Hg)

Thus, the total number of metals that can be extracted by auto-reduction is **3**.

**Final Answer: 3 metals can be extracted by auto-reduction.**

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