Consider the following statements about the troposphere

1. It is the most important zone for weather phenomena.

2. The gradual decrease in the temperature with height is $7.5°\mathrm{C}$ per $\mathrm{km}$.

3. It roughly extends to a height of $8 \mathrm{km}$ near the poles and about $18 \mathrm{km}$ at the equator.

4. The upper limit of the troposphere is called tropopause.

Which of the statement(s) given above are correct?