A patient goes to the doctor with a cold and sore throat and asks for antibiotics. The doctor refuses to prescribe antibiotics to the patient because the illness is caused by which of the following pathogens?

The correct answer is c. 100,000. The pH scale is a logarithmic scale, which means that each change of one pH unit represents a tenfold change in the hydrogen-ion concentration. A pH 4 solution has a hydrogen-ion concentration that is 10^5 (or 100,000) times greater than that of a pH 9 solution.

A. 0.00001 is the hydrogen-ion concentration of a pH 9 solution as compared with a pH 4 solution.

B. 5 is the difference in pH units between a pH 4 solution and a pH 9 solution.

D. 50 is not the correct answer.

The statement "Experiments cannot validate hypotheses, only falsify them" can be restated as "A hypothesis that has not been falsified remains provisional." This means that a hypothesis is considered valid until it is disproved by experimental evidence. However, even if a hypothesis has not been falsified, it is still considered provisional and subject to further testing and scrutiny.

A. "Until disproved, an explanation for an observation is valid" is similar to the correct answer but does not capture the provisional nature of a hypothesis.

B. "Certain concepts cannot be subjected to direct experimentation" is not a restatement of the original statement.

D. "Proving a hypothesis exempts it from further testing" is incorrect because no hypothesis can be definitively proven and all hypotheses are subject to further testing and scrutiny.