Leap Year:
A leap year is a year that is exactly divisible by 4, except for years that are exactly divisible by 100. However, years that are exactly divisible by 400 are leap years.

Divisibility Rules:
To determine if a number is divisible by another number, we can use divisibility rules. These rules help us identify if a number can be divided exactly without leaving any remainder.

Divisibility by 2:
- A number is divisible by 2 if its last digit is 0, 2, 4, 6, or 8. For example, 10, 14, 26, 32, and 48 are all divisible by 2.

Divisibility by 3:
- A number is divisible by 3 if the sum of its digits is divisible by 3. For example, the sum of digits in 12 (1 + 2 = 3) and 24 (2 + 4 = 6) is divisible by 3.

Divisibility by 5:
- A number is divisible by 5 if its last digit is 0 or 5. For example, 10, 15, 20, 25, and 30 are all divisible by 5.

Divisibility by 4:
- A number is divisible by 4 if the number formed by its last two digits is divisible by 4. For example, 12, 16, 24, 28, and 32 are all divisible by 4.

Leap Year and Divisibility:
Based on the above divisibility rules, we can determine which numbers divide a leap year exactly.

- Divisibility by 2: Since a leap year is divisible by 4, it will also be divisible by 2. Therefore, option 'A' is correct.
- Divisibility by 3: A leap year may or may not be divisible by 3. Therefore, option 'B' is not necessarily correct.
- Divisibility by 5: A leap year is not necessarily divisible by 5. Therefore, option 'C' is not correct.
- Divisibility by 4: A leap year is divisible by 4. Therefore, option 'D' is correct.

Conclusion:
Out of the given options, the number that divides a leap year exactly is 4, making option 'D' the correct answer.