To determine which number is not divisible by 14, we need to check each number for divisibility by both 2 and 7, since 14 is the product of these two primes.

Checking divisibility:

1. 3542:
- Divisibility by 2: 3542 is even, so it is divisible by 2.
- Divisibility by 7:
\[
3542 \div 7 = 505.4286 \text{ (not an integer, so not divisible by 7)}
\]
- Conclusion: 3542 is not divisible by 14.

2. 2086:
- Divisibility by 2: 2086 is even, so it is divisible by 2.
- Divisibility by 7:
\[
2086 \div 7 = 298 \text{ (an integer, so divisible by 7)}
\]
- Conclusion: 2086 is divisible by 14.

3. 1998:
- Divisibility by 2: 1998 is even, so it is divisible by 2.
- Divisibility by 7:
\[
1998 \div 7 = 285.4286 \text{ (not an integer, so not divisible by 7)}
\]
- Conclusion: 1998 is not divisible by 14.

4. 2996:
- Divisibility by 2: 2996 is even, so it is divisible by 2.
- Divisibility by 7:
\[
2996 \div 7 = 428 \text{ (an integer, so divisible by 7)}
\]
- Conclusion: 2996 is divisible by 14.


The number that is not divisible by 14 is 1998. However, the closest option among the choices provided is C. 1998.