Which of the following numbers is the smallest?

The smallest number among the given options is -1 because it is a negative number, which means it is less than all positive numbers and zero. In the number line, negative numbers are found to the left of zero, indicating that they are smaller in value.

When comparing -1 with the other choices, 0, 1, and 0.5 are all either zero or positive numbers, making them larger than -1. This establishes that -1 is the smallest of the four numbers presented. Understanding the concept of negative versus positive values on the number line is crucial for determining the smallest or largest numbers in comparisons like this one.