"Is it the right answer?"
Translation:Czy to dobra odpowiedź?
I assume you are talking about "nouns ending with -a" rule. It helps, but this is not the only rule to watch out for. There are also many feminine nouns that end with a soft consonant -(ś)ć/-dź.
Some feminine words are, in fact, exception to the rules, for example „noc” or „mysz”, but there aren't many of those.