(d) In which layer of the atmosphere do airplanes fly? (i) Mesosphere (ii) Exosphere
(iii) Troposphere
(iv) Tropopause​

Troposphere

Explanation:

Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below. The stratosphere is very dry; the air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere.