Nmdcat Practice Paper from PMDC Syllabus | mosaicbro.com

Nmdcat Practice Paper from PMDC Syllabus

7 of 197 questions (Page 23 of 29)

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155 If a radioactive sample has a half-life of about 7.5 days. After 15 days the remaining sample of its original is:
Correct Answer: C
Explanation: After 15 days (2 half-lives), the remaining sample is (1/2)^2 = 1/4 or 25% of the original.
156 The half-life and decay constant for a stable isotopes are respectively given by:
Correct Answer: C
Explanation: Stable isotopes do not decay, so their half-life is infinite and decay constant is zero.
157 The half-life of Na-22 is 3 years. If X grams of these sodium isotopes are initially present, how much is left after 12 years?
Correct Answer: B
Explanation: After 12 years (4 half-lives), the remaining amount is (1/2)^4 = 1/16 of the original.
158 The half-life of radon gas is about 60 sec, this can be changed:
Correct Answer: D
Explanation: The half-life of a radioactive isotope is a constant and cannot be altered by physical or chemical means.
159 Which of the following is the largest unit?
Correct Answer: B
Explanation: 1 Curie = 3.7 x 10^10 Becquerel, making it the largest unit among the options.
160 The radioactive decay law shows that the number of undecayed nuclei:
Correct Answer: C
Explanation: Radioactive decay follows an exponential decay law, where the number of undecayed nuclei decreases exponentially over time.
161 A radioactive substance has a decay constant of λ = 0.693 day^-1. What is its half-life?
Correct Answer: A
Explanation: The half-life (t1/2) is calculated as ln(2)/λ = 0.693/0.693 = 1 day.
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