Which concept of FSA is used in the compiler?a) Lexical analysis b) Parser c) Code generation d) Code optimization

The concept of Finite State Automata (FSA) is used in the compiler during the Lexical analysis phase. So, the answer is a) Lexical analysis.

Here's a step by step explanation:

1. Lexical analysis is the first phase of a compiler. It takes the modified source code from language preprocessors that are written in the form of sentences. The lexical analyzer breaks these syntaxes into a series of tokens, by removing any whitespace or comments in the source code.

2. If the lexical analyzer finds a token invalid, it generates an error. The lexical analyzer works closely with the syntax analyzer. It reads character streams from the source code, checks for legal tokens, and passes the data to the syntax analyzer when it demands.

3. Finite State Automata (FSA) is a mathematical model of computation that it can be in exactly one of a finite number of states at any given time. FSA is used in the lexical analysis phase to recognize tokens as a series of characters.

4. Therefore, the concept of FSA is used in the compiler during the Lexical analysis phase.