Ineed an answer to the photo! asap!

What is the number of moles of chemical units represented by 9.03x10^24? and how do i show work? (dumb it down )

Which is a chemical property of iron? a. it forms iron oxide (rust) when exposed to moisture and air. b. it is a gray–black metal that is hard to the touch. c. it has a melting point of 2795°f (1536°c). d. it is a good conductor of heat

Which of these conditions most likely produces an unstable isotope?