Which one of the following is True?a)Zn is cyclic if and only if n is ...
Explanation:
The given question is related to group theory. Let's understand the options one by one.
a) Zn is cyclic if and only if n is prime: This statement is not true. For example, Z4 is cyclic, but 4 is not a prime number.
b) Every proper subgroup of Zn is cyclic: This statement is true. Let's understand it with an example. Consider Z8 = {0, 1, 2, 3, 4, 5, 6, 7}. Now, let H be a proper subgroup of Z8. H can be {0}, {0, 4}, {0, 2, 4, 6}, or {0, 1, 2, 3, 4, 5, 6, 7}. We can easily verify that all these subgroups are cyclic.
c) Every proper subgroup of S4 is cyclic: This statement is not true. For example, the subgroup generated by (12)(34) in S4 is not cyclic.
d) If every proper subgroup of a group is cyclic, then the group is cyclic: This statement is not true. For example, the Klein four-group is a group in which every proper subgroup is cyclic, but the group itself is not cyclic.
Therefore, the correct answer is option B.
In Summary:
- Option A is false.
- Option B is true.
- Option C is false.
- Option D is false.