Step 1: Understanding the Pathogens and Diseases.
- (P) Streptococcus pyogenes is known to cause Scarlet fever, a condition that results from the release of toxins by the bacteria.
- (Q) Brucella species causes Undulant fever, also known as brucellosis, which leads to cyclical fevers and other symptoms.
- (R) Mycobacterium tuberculosis is the causative agent of Pott’s disease, a form of tuberculosis that affects the spine.
- (S) Escherichia coli is a common cause of Traveler’s diarrhea, often caused by consuming contaminated food or water.
Step 2: Analyzing the options.
- (A) Incorrect, as the matching of Pott’s disease with \textit{Streptococcus pyogenes} and Scarlet fever with \textit{Mycobacterium tuberculosis} is wrong.
- (B) Incorrect, \textit{Mycobacterium tuberculosis} causes Pott’s disease, not Traveler’s diarrhea.
- (C) Correct, this matches each pathogen with its correct disease:
(P) causes Scarlet fever, (Q) causes Undulant fever, (R) causes Pott’s disease, and (S) causes Traveler’s diarrhea.
- (D) Incorrect, as it mismatches \textit{Mycobacterium tuberculosis} with Traveler’s diarrhea.
Step 3: Conclusion.
The correct answer is (C) (P)-(i), (Q)-(iv), (R)-(ii), (S)-(iii).