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Title: GR8677.041
Post by: conantee on January 02, 2010, 01:31:11 PM
41. Which of the following nuclei has the largest binding energy per nucleon? (Consider the most abundant isotope of each element.)
(A) Helium
(B) Carbon
(C) Iron
(D) Uranium
(E) Plutonium


Title: Re: GR8677.041
Post by: conantee on January 02, 2010, 01:36:29 PM
The key idea is that you justify which nuclei has larger binding energy per nucleon from the direction of nuclear reaction. Since nuclei tends to go to state with lower energy (i.e. high binding energy - binding energy is negative in that sense), the product of nuclear reaction tends to have larger binding energy per nucleon than the mother nuclei.

So, (A) and (B) are wrong since they are known as elements for nuclear fusion, e.g. nucleosynthesis in the sun.
(D) and (E) are wrong since they are known as elements for nuclear fission, e.g. in atomic bomb and typical reactor.

The correct answer is (C). 34 of 100 people got the right answer.

Physics behind it: You can check textbook on nuclear physics for more detail. The graph representing binding energy per nucleon has a peak at position corresponding to Iron.