How many molecules or atoms are in 0.0012 moles of aluminum of octane c8h18

1 mole of anything always contains 6.02x10^23 molecules or moles (this is Avogadro's number).  you can use this ratio to find the number of atoms or molecules in any given amount of substance.  Due to that 0.0012 moles can be multiplied by Avogadro's number to find that 0.0012 moles of anything contains 7.224x10^20 atoms or molecules depending on what type of substance you are looking at.  Aluminum consists of atoms while octane consists of molecules.

I hope this helps.  Let me know in the comments if anything is unclear.