Which major atmospheric gas, comprising about 78% of dry air, plays a fundamental role in exert atmospheric pressure, transferring wind force, and causing atmospheric light scattering?

Given below are two statements, one labeled as Assertion (A) and the other as Reason (R): Assertion (A): Water vapor is almost absent in the upper atmosphere. Reason (R): There is an absence of strong vertical turbulent mixing to transport water vapor to very high altitudes. Select the correct answer from the options given below:

Which of the following noble gases constitutes the largest portion of the Earth's atmosphere by volume?