For the same number of carbon atoms, three hydrocarbons P, Q and R have hydrogen in the ratio of 3: 2:1. Which of the following is incorrect about the reactions shown by P, Q and R?

Options

A. P does not undergo addition reactions.
B. Both Q and R decolourise bromine water.
C. Both Q and R give white precipitate with `AgNO_(3)` solution dissolved in `NH_(4)OH`.
D. None of these

Explanation

To solve the question regarding the hydrocarbons P, Q, and R, we need to analyze their structures and the reactions they undergo based on the given hydrogen ratios.

### Step-by-Step Solution:

1. **Identify the Hydrocarbons**:
- Given the ratio of hydrogen atoms in hydrocarbons P, Q, and R is 3:2:1, we can assign the following molecular formulas based on the same number of carbon atoms (let's assume 2 carbon atoms for simplicity):
- P (C2H6): Ethane
- Q (C2H4): Ethene
- R (C2H2): Ethyne

2. **Determine the Type of Hydrocarbons**:
- P (C2H6) is an alkane (single bonds).
- Q (C2H4) is an alkene (double bonds).
- R (C2H2) is an alkyne (triple bonds).

3. **Analyze the Reactions**:
- **P (C2H6)**: As an alkane, it does not undergo addition reactions due to the absence of double or triple bonds.
- **Q (C2H4)**: As an alkene, it can undergo addition reactions and will decolorize bromine water.
- **R (C2H2)**: As an alkyne, it can also undergo addition reactions and will decolorize bromine water.

4. **Evaluate the Statements**:
- The statement "P is not undergoing an addition reaction" is **true**.
- The statement "Q and R decolorize bromine water" is **true**.
- The statement "Both Q and R give a white precipitate with AgNO3 solution dissolved in NH4OH" is **false**. Only alkynes (like R) can form a white precipitate with AgNO3.

5. **Conclusion**:
- The incorrect statement regarding the reactions shown by P, Q, and R is that both Q and R give a white precipitate with AgNO3 solution.

### Final Answer:
The incorrect statement about the reactions shown by P, Q, and R is that both Q and R give a white precipitate with AgNO3 solution dissolved in NH4OH.