The region containing 3/4 of the mass of the atmosphere and the region to which are confined such phenomena as clouds, storms, precipitation and changing weather conditions is called __________.

Correct Answer: Option A — troposphere

The troposphere is the lowest layer of the atmosphere, extending from the surface to the tropopause. It contains approximately 75 to 80 percent of the atmosphere's total mass and is the region where nearly all weather phenomena, including clouds, precipitation, and storms, occur, as defined in Bowditch, Chapter 32.