A piece of zinc (Zn) - a reactive metal - was dropped into a test tube containing a substance. A zinc salt was formed and hydrogen gas was liberated. This is shown in the equation below.
`Zn + ____ ------gt` zinc salt `+ H_(2)` gas
Which of the following can be the substance that zinc was dropped into?
P) water
Q) hydrochloric acid
R) a solution of a zinc salt

Options

A. only P
B. only Q
C. only R
D. either P or R

Answer

To solve the problem, we need to identify which substance zinc (Zn) can react with to produce a zinc salt and hydrogen gas. Let's analyze each option step by step.

### Step 1: Understanding the Reaction
The reaction given is:
\[ \text{Zn} + \text{?} \rightarrow \text{zinc salt} + \text{H}_2 \text{ gas} \]
Here, zinc is reacting with an unknown substance to form a zinc salt and hydrogen gas.

### Step 2: Analyzing the Options
We have three options to consider:
- **P) Water**
- **Q) Hydrochloric Acid**
- **R) A solution of a zinc salt**

### Step 3: Evaluating Each Option
1. **Option P: Water**
- When zinc reacts with water, it typically forms zinc oxide (ZnO) and hydrogen gas, but it does not produce a zinc salt. The reaction is:
\[ \text{Zn} + \text{2H}_2\text{O} \rightarrow \text{ZnO} + \text{H}_2 \]
- Therefore, this option does not lead to the formation of a zinc salt.

2. **Option Q: Hydrochloric Acid (HCl)**
- Zinc reacts with hydrochloric acid to produce zinc chloride (ZnCl₂) and hydrogen gas:
\[ \text{Zn} + \text{2HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \]
- Here, zinc chloride is the zinc salt formed, and hydrogen gas is liberated. This option fits the requirement perfectly.

3. **Option R: A solution of a zinc salt**
- If zinc is added to a solution of a zinc salt, no reaction would occur because zinc cannot displace itself from its own salt. Thus, this option does not produce any new zinc salt or hydrogen gas.

### Step 4: Conclusion
After evaluating all options, the only substance that zinc can react with to produce a zinc salt and hydrogen gas is:
**Q) Hydrochloric Acid (HCl)**

### Final Answer
The substance that zinc was dropped into is **hydrochloric acid (HCl)**.

---