(i) Clearly, $16 > \sqrt{241}$. Prime numbers less than 16 are 2, 3, 5, 7, 11, 13. 241 is not divisible by any of them. $\therefore$ 241 is a prime number. (ii) Clearly, $19 > \sqrt{337}$. Prime numbers less than 19 are 2, 3, 5, 7, 11, 13, 17. 337 is not divisible by any one of them. $\therefore$ 337 is a prime number. (iii) Clearly, $20 > \sqrt{391}$. Prime numbers less than 20 are 2, 3, 5, 7, 11, 13, 17, 19. We find that 391 is divisible by 17. $\therefore$ 391 is not a prime number. (iv) Clearly, $24 > \sqrt{571}$. Prime numbers less than 24 are 2, 3, 5, 7, 11, 13, 17, 19, 23. 571 is not divisible by any one of them. $\therefore$ 571 is a prime number.
Explanation as extracted from the printed page; notation may be imperfect.