Consider the following two sets: Which one of the following options is the CORRECT match from Set X to Set Y ?

Let us analyze the role and output of each compiler phase:

1. P. Lexical Analyzer: Takes the source program as an input stream of characters and produces a sequence of Tokens as output. Hence, $\text{P} \rightarrow 2$.

2. Q. Syntax Analyzer (Parser): Takes the tokens generated by the lexical analyzer and verifies them against the grammar, constructing a Parse Tree (or concrete syntax tree). Hence, $\text{Q} \rightarrow 3$.

3. R. Intermediate Code Generator: Translates the parsed structure into an intermediate representation such as an Abstract Syntax Tree (AST), Directed Acyclic Graph (DAG), or Three-Address Code (TAC). Hence, $\text{R} \rightarrow 1$.

4. S. Code Optimizer: Implements machine-independent optimizations, including Constant Folding (evaluating constant expressions at compile time rather than execution time), constant propagation, and dead-code elimination. Hence, $\text{S} \rightarrow 4$.

Therefore, the correct mapping is:

This matches Option (B).