A prime number is a natural number that only has two divisors: itself and 1. In other words, the quotient of the division is a natural number.
Knowing this, let's analize the numbers we were given:
2 is a prime number, since it can only be divided by itself and 1.
21 is not a prime number, since it can be divided by itself, 1, 2, 3 and 7.
8 is not a prime number, since it can be divided by itself, 1, 2 and 4.
29 is a prime number since it can only be divided by itself and 1.
83 is a prime number since it can only be divided by itself and 1.
Finally, 49 is not a prime number since it can be divided by itself, 1 and 7.
In conclusion, the prime numbers from the given list are 2, 29 and 83.