Final answer:
To round off 0.0015 to one significant figure, the correct rounded value is 0.001.
Step-by-step explanation:
To round off 0.0015 to one significant figure, we need to consider the first non-zero digit. In this case, the first non-zero digit is 1, so the rounded value will be the closest number to 0.0015 with only one significant figure. The correct rounded value is 0.001 (option a).