5. What is chemical formula of table salt?
a. NaCl
b. ClNa
c. Na2Cl
d. NaCl2

6. Which of the following is not a pure substance?
a. hydrogen
b. oxygen
c. water
d. milk

7. Which substance can be decomposed by a chemical change?
a. carbon
b. boron
c. magnesium
d. methanol

8. Which substance cannot be decomposed by a chemical change?
a. water
b. carbon
c. citric acid
d. carbon dioxide​