1. Which of the following is a pure substance?
(a) Air
(b) Salt water
(c) Iron
(d) Sugar solution
2.The smallest particle of an element that can exist independently is called:
(a) Molecule
(b) Atom
(c) Ion
(d) Electron
3. The process of converting a solid directly into a gas is called:
(a) Sublimation
(b) Evaporation
(c) Condensation
(d) Melting