Question

Which of the following provides evidence that a chemical change has taken place?

a). The original substance can be recovered by physical processes
b). A gas is formed when tow liquids are mixed
c). Some pieces of substances get smaller or disappear
d). One substance dissolves in another

Answer 1

Answer : Option B) A gas is formed when two liquids are mixed.

Explanation : In this example a gas is forming as a result of mixing two liquids, so, changing of state can be clearly noticed, also there is a new substance which is produced and the reaction is also irreversible (i.e. it cannot be easily recovered to the starting reactants by any physical process). Hence, Option B is correct answer.