Atomic Nucleus|. Practice MCQs Physics for Mdcat By Engr. Kamran Soomro | mosaicbro.com

Atomic Nucleus|. Practice MCQs Physics for Mdcat By Engr. Kamran Soomro

7 of 114 questions (Page 11 of 17)

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71 The energy of an electron revolving in the first orbit of hydrogen atom is:
Correct Answer: D
Explanation: Ground state energy of hydrogen electron = $-13.6\text{eV}$.
72 A gram mole of any substance contains:
Correct Answer: C
Explanation: Avogadro's number = $6.022 \times 10^{23}$ entities per mole.
73 The half life of phosphorus -32 is 15 days. A given mass of phosphorus-32 will be reduced to $\frac{1}{2}$ of its original mass in:
Correct Answer: B
Explanation: After 2 half-lives (30 days), mass reduces to $\frac{1}{4}$; question likely intends $\frac{1}{4}$ (answer b).
74 What percent of original radioactive atoms left after five half lives?
Correct Answer: A
Explanation: After 5 half-lives, remaining fraction = $(\frac{1}{2})^5 = \frac{1}{32} \approx 3\%$.
75 Radioactivity is:
Correct Answer: B
Explanation: Radioactivity is the spontaneous emission of radiation by unstable nuclei.
76 Gamma rays carry a charge:
Correct Answer: D
Explanation: Gamma rays are neutral photons.
77 Phenomenon of radioactivity is due to disintegration of:
Correct Answer: A
Explanation: Radioactivity results from nuclear instability.
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