Which phase of compiler generates stream of atoms ?

Answer: Lexical Analysis.

Explanation: Lexical analysis (also called scanning) reads the raw source characters and groups them into a stream of tokens (often called atoms).

• What the lexical analyzer produces: tokens such as identifiers, keywords, operators, literals, and punctuation.

• How those tokens are used: the parser (syntax analysis) consumes the token stream to build a parse tree or abstract syntax tree.

• Why other phases are incorrect: code generation produces target code from an intermediate representation, and code optimization improves code quality; neither produces the initial token stream.