Answer
0.75 M NaF solution.
Work Step by Step
$C_{1}=6.0\,M$
$V_{1}=0.25\,L$
$V_{2}=2.0\,L$
Rearranging the dilute expression $C_{1}V_{1}=C_{2}V_{2}$, we get
$C_{2}=\frac{C_{1}V_{1}}{V_{2}}=\frac{6.0\,M\times0.25\,L}{2.0\,L}=0.75\,M$