Which of the following is an incorrect statement?

Options

A. A threshold stimulus is required for the opening of voltage gated channels
B. As soon as threshold stimulus is applied, it causes depolarisation of the entire axonal membrane simultaneously
C. In myelinated nerve fibre, the nerve impulse does not travel as continuous wave of depolarisation due to presence of myelin sheath
D. Initially, polarity of neural membrane is reversed only at the site where threshold stimulus is applied

Answer

To determine which statement is incorrect, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A**: "The sixth mass extinction episode is caused anthropogenically and it is 10 times faster than the rate of the natural extinctions which had taken place in the previous five episodes."
- Analysis: The sixth mass extinction is indeed caused by human activities (anthropogenic). However, it is estimated to be 100 to 1000 times faster than the natural extinction rates of the previous five episodes, not just 10 times. Therefore, this statement is incorrect.

2. **Statement B**: "Passenger Pigeon has become extinct due to over-exploitation of humans."
- Analysis: This statement is correct. The Passenger Pigeon was indeed driven to extinction primarily due to overhunting and habitat destruction caused by humans.

3. **Statement C**: "Norway has lower ecosystem diversity than India."
- Analysis: This statement is also correct. India has a much greater variety of ecosystems (such as tropical forests, deserts, coral reefs, etc.) compared to Norway, which has a more limited range of ecosystems.

4. **Statement D**: "More than 50,000 varieties of mango occur in India."
- Analysis: This statement is incorrect. India is known for having around 1,000 varieties of mango, while the figure of 50,000 refers to the strains of rice found in India.

### Conclusion:
From the analysis, both Statement A and Statement D are incorrect. However, since the question asks for one incorrect statement, we can conclude that Statement A is the main focus of the question regarding the incorrectness of the mass extinction rate.

### Final Answer:
The incorrect statement is **Statement A**.

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