Neutral ligand means ligand with no charge on it.

Example: H₂O, NH₃, CO, C₂ H₄...

ONO^- has a charge on it, therefore it is not a neutral ligand.

The sum of coordination number and oxidation number of the metal M in the complex [M(en)₂(C₂O₄)]Cl (where (en) is ethylenediamine) is 9. The coordination number is 6 as en and C₂O₄ are bidentate ligands.

Let X be the oxidation number of M.

X + 2(0) −2 = +1

X = +3

Thus, the oxidation number is 3.

Hence, the sum of coordination number and oxidation number of the metal M is 6 + 3 = 9.

In chelation, ring formation occurs because two atoms from the same ligand coordinate with the metal atom. This cannot happen if the ligand is monodentate.

Oxalate is a bidentate ligand so it forms a chelate. It can coordinate with both of its negatively charged O atoms.

Acetate, cyanide and ammonia are monodentate ligands. They do not form chelates.

The I.U.P.A.C name of the coordination compound K₃ [Fe (CN)₆] is Potassium hexacyanoferrate(III).

In this complex, there are six CN so they are named hexacyano and the cyanide ligand has −1 charge. So the iron overall has −3 charge, so the name of the central metal atom ends with -ate followed by the charge in roman letters.

Thus, the name of the complex is Potassium hexacyanoferrate(III).

Iron carbonyl, Fe(CO)₅ is mononuclear. In Fe(CO)₅, one Fe atom is surrounded by 5 CO ligands. Mononuclear complexes are those complexes in which one metal atom/ion is surrounded by ligands.

Primary valency is ionizable according to Werner's theory of coordination compounds. 

According to Werner's theory, a coordination compound has two different types of valency, primary and secondary. The primary valency or the ionizable valency is satisfied by the negatively charged ions in the solution.

Primary valency is ionizable and is satisfied by the negative charges whereas Secondary valency is non-ionizable and is satisfied by the positive charged or neutral species in the solution. The primary valency corresponds to the oxidation state of the metal ion.

The secondary valency corresponds to the coordination number of the metal complex. The molecules or ions that satisfy the secondary valency are called ligands and they can be either negatively charged or neutral.

For example, in [Cu (NH₃)₄] SO₄ primary valency is 2 and secondary valency is 4. Secondary valence refers to coordination number. Since copper is coordinated to 4 ammonia ligands, secondary valence is 4. Primary valence is satisfied by anions. Since sulphate ion has -2 charge, primary valence is 2.

Phenol on heating with zinc dust forms benzene.

Anthracene is a solid polycyclic aromatic hydrocarbon, consisting of three fused benzene rings.

Naphthalene is an organic compound with formula C₁₀H₈. It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odour that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, the structure of naphthalene consists of a fused pair of benzene rings. It is best known as the main ingredient of traditional mothballs.

Benzene reacts with phosgene to form benzoyl chloride. It is an example of Friedel Craft's reaction and is carried out in the presence of AlCl₃(Lewis acid) as a catalyst.