How many moles are in 19.82 g Mg?

The rock in a lead ore deposit contains 89 % pbs by mass. how many kilograms of the rock must be processed to obtain 1.5 kg of pb?

Iknow #2 is d. i just need to know why

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?