Final answer:
To determine the correct sign, we must understand that 4.0 × 10⁰ equals 4.0 and 4.0 × 10¹ equals 40. Hence, 4.0 is less than 40, and the correct sign is '<'.
Step-by-step explanation:
The question is asking which sign should be used in the scientific notation to make the statement true when comparing 4.0 × 10⁰ and 4.0 × 10¹.
In scientific notation, the exponent on the 10 indicates the number of places to move the decimal point. The exponent of zero means that the value of 10 to the zeroth power is 1, and thus 4.0 × 10⁰ equals 4.0. On the other hand, 4.0 × 10¹ or 4.0 × 10 equals 40. Therefore, the correct sign to make the statement true would be < (less than), as 4.0 is less than 40.