The difference between the largest number of 3-digits and the smallest number of 3-digits formed by the digits 3, 0 and 8 is

1. 495

2. 765

3. 522

4. 450

To make the largest number, arrange the digits in descending order: 8, 3, 0.

The largest number = 830.

To make the smallest 3-digit number, the hundreds digit cannot be 0. So, place the next smallest digit (3) in the hundreds place, followed by the remaining digits in ascending order (0, 8).

The smallest number = 308.

Difference = Largest number - Smallest number

= 830 - 308

= 522.

Hence, option 3 is the correct option.