Which conditional statement is used to execute a block of code only if a specified condition is true?

The if statement is the correct choice because it is specifically designed to execute a block of code only when a given condition evaluates to true. It allows for decision-making in programming by checking the condition, and if that condition is satisfied, the code within the block will run. This basic structure enables programmers to control the flow of execution based on certain criteria.

On the other hand, a switch statement is used for multi-way branching based on the value of a variable, making it less suited for simple true/false checks. A while loop and a for loop both repeatedly execute a block of code based on a condition or a sequence, but they are not conditional statements in the same way that an if statement is. They focus on repetition rather than conditional execution based solely on truth.