The correct options are
A energy stored in the capacitor decreases
B the potential difference between the plates decreases
C the capacitance increases
As battery is disconnected so charge q is constant.
The parallel plate capacitance is C=Aϵ0dorC∝1d
If the capacitor are brought closer, d will decrease so C will increase.
Energy stored in capacitor is U=q22CorU∝1C
As C increases, so U will decrease.
The electric field between plates is E=qAϵ0
As q is constant so E becomes unchanged.
Potential difference between the plates is V=EdorV∝d
As d decreases so V will decrease.