Final answer:
The number 4.0 × 10⁵ has two significant figures: 4 and 0.
Step-by-step explanation:
Significant figures (also known as significant digits) are digits in a numerical value that carry meaningful information about the precision of the measurement. They include all certain digits and the first uncertain digit.
The number 4.0 × 10⁵ has two significant figures.
In scientific notation, all significant figures are listed explicitly. In this case, the number 4.0 × 10⁵ has two significant figures: 4 and 0.