Question:

Which of the following is a prime number?

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When checking for primes, test divisibility only up to the square root of the number. This speeds up the process.
Updated On: Aug 12, 2025
  • 19
  • 20
  • 21
  • 22
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The Correct Option is A

Solution and Explanation

Step 1: Definition — A prime number is a number greater than 1 that has no positive divisors other than 1 and itself.
Step 2: Check each option: - 19: Divisible only by 1 and 19 → Prime.
- 20: Divisible by 1, 2, 4, 5, 10, and 20 → Composite.
- 21: Divisible by 1, 3, 7, and 21 → Composite.
- 22: Divisible by 1, 2, 11, and 22 → Composite.
Step 3: Therefore, the only prime number in the list is 19.
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