In the fifth bar, there is a natural sign preceding the C note. If I am reading the key signature correctly, there is only one sharp, which is F note. If I am correct, what is the purpose for making C natural, when it already is.
It is called a guide or courtesy accidental. It is not required since the C# accidental in bar 3 automatically cancels at the end of the bar but sometimes composers, arrangers or copyists put them in to remind the player the accidental is canceled. It is typically done in the bar immediately following the bar with the accidental though, not as often 2 bars later like in this excerpt.