Syntax is the correct answer for the above question.
Explanation:
When any user wants to write any program (which can be called a set of instructions), then he needs to follow the syntax of that programming language.
Programming language is a set of rules defined by the generator of that program. In any programming language, there is a compiler that understands the meaning of any line.
The above question asked what is a set of rules in any programming language. The answer is Syntax.
