How do you define a variable in Kotlin?

In Kotlin, defining a variable depends on whether you want it to be mutable or immutable. The keywords used for this purpose are 'val' and 'var.'

When you declare a variable with 'val,' it means that the variable is read-only and cannot be reassigned after its initial assignment. This is comparable to a constant in many other programming languages. On the other hand, if you use 'var,' the variable can be changed after its declaration, allowing you to reassign it to a different value later on. This duality gives developers flexibility in managing data, ensuring that one can use immutable references where appropriate to maintain stability and predictability in the code.

Thus, the option that mentions 'val' for immutable variables and 'var' for mutable variables accurately captures the Kotlin approach to variable declaration, making it the correct choice.