15. Which of the following is a pure substance? A) blood B) block of aluminum C) air D) orange juice 16. Which of the following is an example of a homogeneous mixture? A) sand B) copper C) air D) sugar 17. What is another name for a homogeneous mixture? A) pure substance B) compound C) solution D) element 18. Dirt is an example of a(n) A) homogeneous mixture B) heterogeneous mixture C) compound D) element 19. Which of the following is an example of a heterogeneous mixture? A) seawater B) steel C) milk D) chicken noodle soup 20. What is the name given to the element with the symbol "P"? A) polonium B) protactinium C) phosphorus D) palladium