Bidentate and negatively charged ligands are molecules or ions that have two donor atoms capable of forming two coordination bonds with a central metal ion and carry a negative charge. These ligands play a crucial role in coordination chemistry as they can form stable complexes with metal ions due to their ability to donate electrons.

The given options for bidentate and negatively charged ligands are:

a) Acetylacetonate (acac):
- Acetylacetonate is a bidentate ligand that contains two oxygen atoms capable of donating a pair of electrons to form coordination bonds with a metal ion.
- It carries a negative charge due to the presence of two additional electron-donating groups (CH3) on the molecule.
- The negatively charged acetylacetonate ion (acac-) can coordinate with a metal ion by donating its lone pairs of electrons to form stable complexes.

b) Propylene diamine (pn):
- Propylene diamine is a bidentate ligand that contains two nitrogen atoms capable of donating a pair of electrons to form coordination bonds with a metal ion.
- However, it does not carry a negative charge.

c) Ethylene diamine (en):
- Ethylene diamine is a bidentate ligand that contains two nitrogen atoms capable of donating a pair of electrons to form coordination bonds with a metal ion.
- However, it does not carry a negative charge.

d) Bipyridyl (bip):
- Bipyridyl is a bidentate ligand that contains two nitrogen atoms capable of donating a pair of electrons to form coordination bonds with a metal ion.
- It does not carry a negative charge.

Among the given options, only acetylacetonate (acac) satisfies both criteria of being bidentate and negatively charged. It has two oxygen atoms capable of forming coordination bonds and carries a negative charge due to the presence of additional electron-donating groups. Therefore, option 'A' is the correct answer.

This information is crucial in understanding the chemical behavior and reactivity of coordination compounds, as different ligands can influence the properties and stability of the resulting complexes.