Equation for the formation of a magnesium ion

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

Aroller coaster is traveling at 13 mi./s when you purchase a hill that is 400 m long and down the hill exonerate at 4.0 m/s squared what is the final velocity of the posterior found your answer to the nearest number

Ab c or d ? i’m not sure what the answer is