The difference between the place value and face value of a digit in a number is an important concept in mathematics. Let's understand the difference between place value and face value and apply it to the given number, 3451.

Place Value:
The place value of a digit in a number indicates the value of the digit based on its position in the number. Each digit in a number has a specific place value. The place value starts from the rightmost digit, which is the units place, and increases as we move towards the left. The place values are multiples of powers of 10.

In the number 3451:
- The place value of 4 is 4 × 1000 = 4000 (because 4 is in the thousands place).
- The place value of 3 is 3 × 100 = 300 (because 3 is in the hundreds place).
- The place value of 5 is 5 × 10 = 50 (because 5 is in the tens place).
- The place value of 1 is 1 × 1 = 1 (because 1 is in the units place).

Face Value:
The face value of a digit in a number represents the actual value of the digit. It is the numerical value that the digit holds on its own, regardless of its position in the number.

In the number 3451:
- The face value of 4 is 4.
- The face value of 3 is 3.
- The face value of 5 is 5.
- The face value of 1 is 1.

Difference between Place Value and Face Value of 4 in 3451:
The difference between the place value and face value of 4 in the number 3451 can be calculated by subtracting the face value from the place value.

- Place value of 4 = 4000
- Face value of 4 = 4

4000 - 4 = 3996

Thus, the difference between the place value and face value of 4 in the number 3451 is 3996, which corresponds to option 'B' in the given answer choices.