Cyclopentadiene is the compound shown. Which statements are correct? Select all that apply.

1. AThe cation formed by hydride removal is more stable than the anion formed by proton removal.
2. BIts pKa (about 16) is far lower than that of cyclopentane because of the aromatic stabilisation of the conjugate base.
3. CRemoval of a proton from its CH${}_2$ group gives a planar cyclic anion with 6 pi electrons, which is aromatic.
4. DRemoval of a hydride ion from its CH${}_2$ group gives a planar cyclic cation with 4 pi electrons, which is antiaromatic.