Answer
0.50 M $HNO_{3}$ solution.
Work Step by Step
$C_{1}=4.0\,M$
$V_{1}=1.0\,L$
$V_{2}=8.0\,L$
Rearranging the dilute expression $C_{1}V_{1}=C_{2}V_{2}$, we get
$C_{2}=\frac{C_{1}V_{1}}{V_{2}}=\frac{4.0\,M\times1.0\,L}{8.0\,L}=0.50\,M$