How can you tell if a substance is a mixture or a compound

Harvey kept a balloon with a volume of 348 milliliters at 25.0˚c inside a freezer for a night.  when he took it out, its new volume was 322 milliliters, but its pressure was the same.  if the final temperature of the balloon is the same as the freezer’s, what is the temperature of the freezer? the temperature of the freezer is  kelvins.

How many moles of magnesium is 3.01 x10^22 atoms of magnesium?

What diagram shows the ionic compound of magnesium oxide