To find the largest 4-digit even number that can be formed using the digits 2, 3, 5, and 6, we need to consider the place values of each digit.

Let's analyze the given options:

a) 3256
b) 6523
c) 6532
d) 2356

We can start by comparing the thousands places of each option. Since we want the largest number, the digit in the thousands place should be the greatest among the options.

- Comparing the thousands places:
- Option a) has 3 in the thousands place.
- Option b) has 6 in the thousands place.
- Option c) has 6 in the thousands place.
- Option d) has 2 in the thousands place.

Since option c) has the greatest digit in the thousands place (6), we can eliminate options a), b), and d) because they cannot form the largest 4-digit even number.

Now, let's compare the hundreds places of the remaining options:

- Comparing the hundreds places:
- Option a) has 2 in the hundreds place.
- Option b) has 5 in the hundreds place.
- Option c) has 5 in the hundreds place.

Since option c) has the greatest digit in the hundreds place (5), we can eliminate options a) and b) because they cannot form the largest 4-digit even number.

Now, let's compare the tens places of the remaining options:

- Comparing the tens places:
- Option a) has 5 in the tens place.
- Option c) has 3 in the tens place.

Since option a) has the greatest digit in the tens place (5), we can eliminate option c) because it cannot form the largest 4-digit even number.

Finally, let's compare the units places of the remaining options:

- Comparing the units places:
- Option a) has 6 in the units place.

Therefore, the largest 4-digit even number that can be formed using the digits 2, 3, 5, and 6 is 3256, which corresponds to option a).

Largest 4-digit even number using the given digits = 6532