Answer
An Elliptical cylinder along y-axis as shown in $\bf{Graph(b)}$
Work Step by Step
Given: $x^2+2z^2=8$ ....(1)
Re-write as:
$\dfrac{x^2}{(2 \sqrt 2)^2}+\dfrac{z^2}{(2)^2}=1$ ...(2)
Hence, the equation (2) shows a graph for an Elliptical cylinder along y-axis as shown in $\bf{Graph(b)}$
