A parallel plate capacitor is charges by being connected to a battery and is kept connected to the battery.  The electric field between the plates is E₁.  Now the separation between the plates is doubled and the electric field between the plates is E₂ Then E₁/E₂ is

 2

$E_1 = \frac{V}{d}$

$E_2 = \frac{V}{2d}$

$ \frac{E_1}{E_2} = 2$