Deciding the class of certain languages
The answers are correct, but when proving that a language is not regular, or not context-free, it is not enough to show that one attempt does not work. You have to use tools like pumping lemma. For context-free languages, there is a version of pumping lemma which should work here: http://en.wikipedia.org/wiki/Pumping_lemma_for_context-free_languages

Also it's a detail, but in your last argument, $2i+j+l$ is not any number $&gt;0$, it is at least $5$, since $j&gt;l$ and $i,l,k&gt;0$. So your language is $\{(210)^n : n\geq 5\}$, which is indeed regular.