You've just found the huge task in learning kanji!
because Japanese words existed before Chinese characters were used to write them, Japanese readings exist for kanji characters.
Then the Chinese reading also came to be used especially in compounds when new words got introduced.
Then...
the kanji came into the Japanese language at several times in history so there can be several Chinese readings.
And...
sometimes there are asigned readings just to make things difficult!
There's an explanation here
http://www.japanesepod101.com/wp-conten ... nation.php
Therefore a single kanji can be read in many different ways.
The convention in dictionaries and lists is to write the kunyomi (Japanese reading) in hiragana, and the onyomi (Chinese reading) in katakana.
so usually country will be written 国 and read as くに
but in a compound like 中国 (China, middle kingdom) it is read as ごく, ちゅうごく in this case.
so they are both correct!
here's an interesting one -->
腹切 is harakiri (ritual suicide) "stomach cut"
but reverse the kanji and you get
切腹 seppuku (ritual suicide) "cut stomach"
"pure" katakana words tend to be loan words often from English
タクシー taxi
レストラン resterant
ペン pen
コップ glass (from the dutch kop apparently)
サャツ shirt
イギリス England
バッグ bag
パン bread (french pan)
ズボン trousers (french again )