What to do when Samsung Galaxy Core 2 get problem in internet connection and Facebook app?

my Samsung galaxy core 2. has a major problemm. . some time its not connecting to internet. some time when its connected. when I open facebook app it opens I log in. after that it gets frzzen.... again. some time when I open opera. it working... but some time it also gets hang.. plz tell me a way to fix this mess

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