The Assertion (A) states that the thickness of the atmosphere is maximum over the Equator. This is true because the Earth is an oblate sphere with maximum bulge at the equator due to its rotation. This means the atmosphere is indeed thicker at the equator.

The Reason (R) for this, given, is that high insolation (incoming solar radiation) and strong convection currents occur over the Equator. This is also a true statement. The equator receives the maximum insolation due to the direct rays from the sun. This leads to warming and causes the air to rise, creating strong convection currents. These currents contribute to the thickness of the atmosphere here.

Thus, option 1 is right - Both A and R are individually true, and R is the correct explanation of A. The thickness of the atmosphere around the equator is due to the stronger insolation and convection currents at the equator, as the Reason correctly explains the Assertion.