Step 1: Understanding the Task
The goal is to arrange the four parts to form a meaningful sentence comparing the Himalayas to the Peninsular Block.
Step 2: Finding the Logical Flow
Part P starts forming the subject of the sentence: "the Himalayas along with other Peninsular". This phrase is incomplete.
Part Q completes the subject ("Peninsular mountains") and provides the main verb ("are") and predicate adjectives ("young, weak and flexible in their..."). Thus, P-Q forms a cohesive unit: "the Himalayas along with other Peninsular mountains are young, weak and flexible in their...".
"Flexible in their" needs an object. Part R provides this: "geological structure unlike the rigid and". This continues the description and introduces a comparison. The sequence is now P-Q-R.
The phrase "unlike the rigid and" needs to be completed. Part S, "stable Peninsular Block", completes this comparison, serving as the object of "unlike".
Step 3: Constructing the Final Sentence
The complete sentence reads: "The Himalayas along with other Peninsular mountains are young, weak and flexible in their geological structure unlike the rigid and stable Peninsular Block."
Step 4: Final Answer
The logical and grammatical sequence is PQRS. Therefore, option (C) is the correct answer.