Use the image below to find the density of a ring that has a mass 32g.? orig.-64 beaker with ring-68

Idon't understand what to put on the left lines i'm confused can anyone ?

How many moles of lead are in 1.50 x 10^12 atoms of lead? could you explain the answer as well and not just give it to me i am refreshing for finals and i need to know how to do it

Which of the four hypothetical substances you investigated would be most harmful to living organisms? 50 points!