Mixtures Vocabulary Lesson help ASAP

Hydrogen and helium are both members of?

Why does lightning travel from clouds to the ground?

Determine the moment of the force f about an axis extending between a and c. express the result as a cartesian vector. a is at the origin, c is at (4,3,0) and f = (4i + 12j -3k) lb coming out of b (4,3,-2).