Question

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.
according to the passage, which of the following would cause milk to go bad?
choose one option
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

Explanation:

The passage states that when too much acid (produced by bacteria digesting sugar in milk) is present, a chemical change occurs in the milk (it goes bad). Option A is incorrect as it's not just any bacteria presence but excessive acid from bacteria. Option B is wrong because bacteria are involved in the process (not their absence). Option C is not mentioned as a cause. Option D aligns with the passage's description of the cause (too much acid from bacteria).

Answer:

D. too much acid produced by bacteria