These questions are the questions that I need help on...

20 in the formula no3, what does the subscript 3 mean?

Consider the last statement in the prompt: "people take such environmental factors into account in their choices when deciding where to live." do all people have a choice as to where they live? what factor plays a key role in this decision and may therefore play a large role in determining quality of life?

What types of energy transfers and energy transportations are involved in the domino chain reaction?