4. A
because PbCl2 is an ionic compound and it's solid, so it's a substance.
It cannot be mixture, because it's a pure molecule.
5. D
despite that both substances are gases, colorless they are different molecules, so they should have different either chemical and physical properties
6. C
this substance made from W atoms and others are made from molecules
THE DEFINITION OF PHYSICAL CHANGE: Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. Physical changes are used to separate mixtures into their component compounds, but can not usually be used to separate compounds into chemical elements or simpler compounds. so the answer is that the form of the sugar is changing in water but if you boiled the water till its all evaporated all that will be left is the sugar
Einstein's theory of special relativity sets of the speed of light, 186,000 miles per second (300 million meters per second). ... The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light.
