5 3. Identify each of the following observations as evidence of either a physical change or a
chemical change.
(a) A piece of copper is heated until it melts.
(b) A piece of aluminum corrodes in a solution of acid.
(c) A piece of paper burns in a candle flame.
(d) A piece of plastic is stretched until it breaks.
(e) Table salt boils at 1465°C.​

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.

answer: option (a) is the correct answer.

explanation:

the measurement of hydrogen ions in a solution is known as ph.

if ph of a solution is less than 7 then the solution is acidic. if ph of a solution is greater than 7 then the solution is basic.

when the ph of a solution equals 7, then the solution is considered as neutral.

the ph of pure water is 7, therefore, it means that concentration of hydronium ions equals that of hydroxide ions.