• Equatorial Tropopause Altitude: Due to intense solar heating at the equator, powerful convective updrafts lift the tropospheric boundary to an altitude of approximately 16 to 18 km (compared to only 8 to 9 km over the poles).
• Lapse Rate & Cooling: As air rises through the troposphere, temperature declines at the environmental lapse rate (~$6.5^\circ\text{C/km}$). Because the tropospheric column is tallest at the equator, adiabatic cooling continues to greater heights.
• Equatorial Temperature Range: At the equatorial tropopause, temperatures reach between -70°C and -75°C (occasionally dipping below -80°C), making the equatorial tropopause significantly colder than the polar tropopause (which averages around -45°C to -55°C).

Correct option: (2) -70°C to -75°C