To find the value of x, we can use the given information.

We are given that x = y = 2z and xyz = 256.

Since x = y, we can substitute x with y in the second equation:

xy * z = 256

(x * x) * z = 256

x^2 * z = 256

Now, we know that x = 2z, so we can substitute x in terms of z:

(2z)^2 * z = 256

4z^2 * z = 256

4z^3 = 256

To solve for z, we can divide both sides of the equation by 4:

z^3 = 64

Taking the cube root of both sides gives us:

z = 4

Now that we know the value of z, we can substitute it back into the equation x = y = 2z:

x = y = 2 * 4

x = y = 8

Therefore, the value of x is 8.

The answer is: C. 8