A chemical change takes place when milk goes bad. Normally, bacteria in milk digest sugar and produce an acid. When too much of that acid is produced, however, a chemical change occurs in the milk and leaves lots of evidence. One of the first ways people check milk is by smelling the carton. The distinct sour smell is evidence of the chemical change. If it smells sour, it will also have a lower pH level. It might also have a change in color and appear yellowish. Rotten milk might also have lumps in it. Those lumps are an example of a precipitate, a solid formed in a liquid solution. Forming a mixture by combining two liquids—like water and juice—or a solid and a liquid—like sugar and coffee—is just a physical change. But when a new solid forms and separates from within a liquid mixture, like chunks in milk, a chemical change has occurred.

Question

According to the passage, which of the following would cause milk to go bad?

A
the presence of any bacteria

B
the absence of any bacteria

C
not enough sugar for bacteria to eat

D
too much acid produced by bacteria

Answer 1

D
too much acid produced by bacteria