Amongst the following the metals which become passive when dipped in conc. `HNO_(3)` are Sn, Pb, Fe, Cr, Zn, Ni, Hg, Al, Cu.

Explanation

To determine which metals become passive when dipped in concentrated nitric acid (HNO₃), we need to analyze the behavior of each metal in the presence of this strong oxidizing agent.

### Step-by-Step Solution:

1. **Understanding Passivation**:
- Passivation is the process by which a metal becomes less reactive due to the formation of a protective oxide layer on its surface. This layer prevents further corrosion and reaction with the acid.

2. **List of Metals**:
- The metals given are: Sn (Tin), Pb (Lead), Fe (Iron), Cr (Chromium), Zn (Zinc), Ni (Nickel), Hg (Mercury), Al (Aluminum), Cu (Copper).

3. **Analyzing Each Metal**:
- **Sn (Tin)**: Does not form a protective oxide layer in concentrated HNO₃.
- **Pb (Lead)**: Forms a layer but is not considered passive in concentrated HNO₃.
- **Fe (Iron)**: Forms a passive layer of iron oxide (Fe₃O₄) when reacted with concentrated HNO₃.
- **Cr (Chromium)**: Forms a passive layer of chromium oxide (Cr₂O₃) in concentrated HNO₃.
- **Zn (Zinc)**: Does not become passive; it reacts with HNO₃.
- **Ni (Nickel)**: Forms a passive layer of nickel oxide (NiO) in concentrated HNO₃.
- **Hg (Mercury)**: Does not become passive; it reacts with HNO₃.
- **Al (Aluminum)**: Forms a passive layer of aluminum oxide (Al₂O₃) in concentrated HNO₃.
- **Cu (Copper)**: Does not become passive; it reacts with HNO₃.

4. **Identifying Passive Metals**:
- From the analysis, the metals that become passive when dipped in concentrated HNO₃ are:
- Fe (Iron)
- Cr (Chromium)
- Ni (Nickel)
- Al (Aluminum)

5. **Conclusion**:
- The metals that become passive when dipped in concentrated HNO₃ are **Fe, Cr, Ni, and Al**.

### Final Answer:
The metals that become passive when dipped in concentrated HNO₃ are **Fe, Cr, Ni, and Al**.

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