If $4$kmol of $O2$ and $2$kmol of $N2$ are both at $298K$ and $1$atm and separated by a partition. If the gases are allowed to mix and are assumed to be ideal gas mixture, determine the following

$($assuming no change in $T$ and $P)$:

A$)$ What is the partial pressure of $O2$ in the tank after mixing?

B$)$ What is the change in entropy for $O2(\frac{J}{m}$olK$)$

C$)$ What is the change in entropy for the mixture $(S$ mix $T,P$ in $\frac{J}{m}$olK $)$