Choose the best answer. Which observation suggests that matter exists as very small, moving particles?
A. Metal can be beaten into sheets
B. Solids will melt when heated
C. Some gases are less dense than air, but other gases are denser.
D. The smell of scent soon fills a room when the bottle is opened

3. What happens to the molecules when steam condenses to water at room temperature?
A. Molecules become smaller.
B. Molecules become regularly arranged.
C. Molecules lose energy
D. Molecules move further apart

4. Which of the following is an example of sublimation?
A. Changing ice to water
B. Spread of purple potassium permanganate in water
C. Solid ammonium chloride changing into vapour
D. Hot air rising above a burning candle

5. If a substance is pure
A. the substance must dissolve in water B. the substance must be colourless
C. the substance must melt at any temperature
D. the substance must melt at an exact known temperature

6. Which one of the following could be a pure substance?
A. Yellow crystals that melt over the range 67°C - 72°C.
B. A blue solution.
C. Colourless crystals that melt at 80°C.
D. A green dye that gives blue and yellow spots in a chromatogram​