Which has a larger impact on change in atomic size: moving down one period or moving across a family

Why are people not able to scuba dive in the deep part of the ocean

How have the greenhouse gasses increased from the year 2000 to 2018

How many mmols of tris-hcl are there in 100 ml of a 100 mm tris-hcl buffer solution at ph 8.1? note that the 100 mm refers to the sum of tris and tris-hcl concentrations?