Equation of a plane with intercept $\sqrt{3}$ on z-axis and parallel to XOY plane is :

$z-\sqrt{3}=0$

intercept on z-axis → $\sqrt{3}$

for place with intercepts a, b, e on x, y and z

e.g → $\frac{x}{a}+\frac{y}{b}+\frac{z}{c} = 1$

as place is parallel to XOY

so omitting $\frac{x}{a}$  and  $\frac{y}{b}$

so $\frac{z}{\sqrt{3}} = 1$

$z=\sqrt{3}$

$z-\sqrt{3}=0$