Answer
$div G=f(x,y,z)$; That is, every function $f$ is divergence of some vector field.
Work Step by Step
Suppose we have a vector field $G$ such that $G=\lt g(x,y,z) ,0,0 \gt$
Here, we have $g(x,y,z) =\int_0^x f(t,y,z) dx$
Also, $div F=\dfrac{\partial a}{\partial x}+\dfrac{\partial b}{\partial y}+\dfrac{\partial c}{\partial z}=\dfrac{\partial }{\partial x}[\int_0^x f(t,y,z) dx]+\dfrac{\partial (0)}{\partial y}+\dfrac{\partial (0)}{\partial z}$
This implies that
$div G=f(x,y,z) +0+0=f(x,y,z)$
Hence it has been proved that every function $f$ is divergence of some vector field.
