Explanation:
1). A change that does not bring any difference in chemical composition of a substance are known as a physical change.
For example, shape, size, mass, volume, density, etc of a substance are all physical changes.
And, a change that brings difference in chemical composition of a substance is known as chemical change.
For example, precipitation, reactivity, toxicity etc are chemical changes.
Change in color also depicts a chemical change but not always.
Hence, we can conclude that evidence of a chemical change include change in color.
2). When salt dissolves in water then it is a physical change. This is because salt dissociates into ions and does not chemically combine with water.
A child colors a picture with a crayon is also a physical change since no change in chemical composition is taking place.
Solid iron is heated until it turns into a liquid depicts change in state of substance. Hence, it is a physical change.
A metal is added to an acid and hydrogen gas is formed shows a chemical change as formation of gas only occurs due to change in chemical composition of a substance.
Thus, we can conclude that a metal is added to an acid and hydrogen gas is formed would indicate a chemical change has occurred.
