Which of the following statements is incorrect?

Options

A. Motion of a vehicle on a straight road is not rectilinear motion
B. Motion of honeybees is the example of random motion.
C. Cubit is the length of a forearm.
D. Centigrade is not the SI unit of temperature.

Answer

To determine which statement is incorrect, we need to analyze each statement provided.

1. **Statement 1**: "Motion of a vehicle on a straight road is not rectilinear motion."
- This statement is incorrect because the motion of a vehicle on a straight road is indeed an example of rectilinear motion. Rectilinear motion refers to motion along a straight line.

2. **Statement 2**: "Motion of honey bees is the example of random motion."
- This statement is correct. Honey bees do exhibit random motion as they move around in search of flowers.

3. **Statement 3**: "Qubit is the length of a forearm."
- This statement is incorrect. A qubit is a unit of quantum information, not a measure of length. The length of a forearm is typically measured in centimeters or inches.

4. **Statement 4**: "Centigrade is not the SI unit of temperature."
- This statement is correct. The SI unit of temperature is Kelvin, while Centigrade (or Celsius) is a scale used for temperature measurement but is not the SI unit.

Now, let's summarize the findings:
- Statement 1 is incorrect because a vehicle on a straight road does exhibit rectilinear motion.
- Statement 3 is incorrect because a qubit is not a measure of length.
- Statement 4 is correct as it correctly identifies that Centigrade is not the SI unit.

**Conclusion**: The incorrect statements are Statement 1 and Statement 3. However, since the question asks for one incorrect statement, Statement 1 is the most relevant as it directly relates to motion.

### Final Answer:
The incorrect statement is: "Motion of a vehicle on a straight road is not rectilinear motion."