Misc: [science and technology] what is the lightest known gas?

Questions

"You come to love not by finding the perfect person, but by seeing an imperfect person ----------."- Sam Keen?

"You don't get --------- when everybody sings the same note."- Doug Floyd?

"You get the best out of others when you give the best of -----------."- Harry Firestone?

"------------- is a relentless master. It has no present, only the past rushing into the future. To try to hold fast is to be swept aside."- John fitzgerald Kennedy?

"---------- is a vast early warning system."- Norman Cousins?