Option A:
Does transforming a CFG to Chomsky's normal form make it unambiguous?
The answer is No.
There are inherently ambiguous context-free languages, and like all context-free languages they have grammars in Chomsky's normal form, so transforming a CFG to Chomsky's normal form doesn't necessarily make it unambiguous. For the same reason there is no technique to convert an arbitrary context-free grammar to one which is unambiguous.
Deciding whether a given context-free grammar is ambiguous, or whether a given context-free grammar generates an inherently ambiguous language, is undecidable.
Option B:
For any $n$, it is a finite language with only one string. So, it is regular for every $n$.
Option C:
Take $\text{L}=\left\{a^p \mid p\right.$ is prime $\}$; is non-regular but $\text{L}^*$ is regular.
Option D:
If there's a $10$-state NFA that accepts $\text{L}$ then there's definitely a $1024$-states DFA that accepts $\text{L},$ but cannot say conclude that a $100$ state DFA.
