NCERT Real Numbers MCQs – Proof of Irrationality of √2, √3 & √5
NCERT Real Numbers MCQs – Proof of Irrationality of √2, √3 & √5
Class: 10 | Subject: Mathematics
Chapter 1: Real Numbers
Based on NCERT | As per Latest CBSE Board Examination Pattern
1. The proof that √2 is irrational is based on which method?
Correct Answer: B. Contradiction method
Explanation: We assume √2 is rational and express it as p/q in lowest form. This assumption leads to both p and q being even, which contradicts the condition of lowest form. Hence √2 is irrational.
Explanation: We assume √2 is rational and express it as p/q in lowest form. This assumption leads to both p and q being even, which contradicts the condition of lowest form. Hence √2 is irrational.
2. If √2 = p/q in lowest terms, then p and q must be:
Correct Answer: B. Both even
Explanation: After squaring, we get p² = 2q², meaning p² is even, so p is even. Substituting back shows q is also even, contradicting the lowest form assumption.
Explanation: After squaring, we get p² = 2q², meaning p² is even, so p is even. Substituting back shows q is also even, contradicting the lowest form assumption.
3. If p² is even, then p must be:
Correct Answer: A. Even
Explanation: The square of an odd number is always odd. Therefore, if p² is even, p must be even.
Explanation: The square of an odd number is always odd. Therefore, if p² is even, p must be even.
4. Which statement is true about √3?
Correct Answer: B. It is irrational
Explanation: Using contradiction similar to √2, assuming √3 = p/q leads to contradiction. Hence √3 cannot be written as p/q and is irrational.
Explanation: Using contradiction similar to √2, assuming √3 = p/q leads to contradiction. Hence √3 cannot be written as p/q and is irrational.
5. The decimal expansion of √5 is:
Correct Answer: C. Non-terminating non-repeating
Explanation: Irrational numbers have decimal expansions that are non-terminating and non-repeating. Since √5 is irrational, it follows this pattern.
Explanation: Irrational numbers have decimal expansions that are non-terminating and non-repeating. Since √5 is irrational, it follows this pattern.
6. The contradiction in irrationality proof arises because:
Correct Answer: C. p and q are both divisible by 2
Explanation: This contradicts the assumption that p/q is in lowest terms.
Explanation: This contradicts the assumption that p/q is in lowest terms.
7. Which root is irrational?
Correct Answer: D. √3
Explanation: √4=2, √9=3, √16=4 are integers. √3 is not a perfect square, so it is irrational.
Explanation: √4=2, √9=3, √16=4 are integers. √3 is not a perfect square, so it is irrational.
8. If √2 were rational, it could be written as:
Correct Answer: B. p/q
Explanation: A rational number can always be expressed as p/q where q ≠ 0.
Explanation: A rational number can always be expressed as p/q where q ≠ 0.
9. The square of an odd number is always:
Correct Answer: B. Odd
Explanation: (2n+1)² = 4n²+4n+1 which is odd.
Explanation: (2n+1)² = 4n²+4n+1 which is odd.
10. √2 lies between which two integers?
Correct Answer: B. 1 and 2
Explanation: √2 ≈ 1.414, so it lies between 1 and 2.
Explanation: √2 ≈ 1.414, so it lies between 1 and 2.
11. Which of the following is rational?
Correct Answer: C. √9
Explanation: √9 = 3 which is rational.
Explanation: √9 = 3 which is rational.
12. In proof of √3 irrationality, we get:
Correct Answer: C. Both p and q divisible by 3
Explanation: This contradicts the lowest form assumption.
Explanation: This contradicts the lowest form assumption.
13. √5 is irrational because 5 is:
Correct Answer: A
Explanation: Prime numbers that are not perfect squares have irrational square roots.
Explanation: Prime numbers that are not perfect squares have irrational square roots.
14. Which is NOT irrational?
Correct Answer: C
Explanation: √25 = 5 which is rational.
Explanation: √25 = 5 which is rational.
15. Rational numbers have decimal expansion that is:
Correct Answer: B
Explanation: Rational numbers either terminate or repeat.
Explanation: Rational numbers either terminate or repeat.
16. √3 approximately equals:
Correct Answer: A
Explanation: √3 ≈ 1.732.
Explanation: √3 ≈ 1.732.
17. √5 approximately equals:
Correct Answer: A
Explanation: √5 ≈ 2.236.
Explanation: √5 ≈ 2.236.
18. If p² divisible by 3, then p is:
Correct Answer: B
Explanation: Property used in irrationality proof of √3.
Explanation: Property used in irrationality proof of √3.
19. √2 is an example of:
Correct Answer: C
Explanation: It cannot be expressed as p/q.
Explanation: It cannot be expressed as p/q.
20. The assumption √2 = p/q must be in:
Correct Answer: A
Explanation: The fraction must be in lowest form for contradiction method to work properly.
Explanation: The fraction must be in lowest form for contradiction method to work properly.
