Throughput of pure aloha ,S=G × $e^{-2G}$. Where G is the average no. Of frames generated by system during one frame transmission time.
Transmission time =$\frac{frame size} {bandwidth}$=$\frac{1000 bits}{1Mbps}$=1 ms.
If a station create 10 frames per second means 100 stations(system) will create $1$ frame per millisecond ,so G= $1$
$S = G×e^{-2G} = 0.135$
$0.135 \times 1Mbps = 135 Kbps$