Sodium tetrafluoridodihydroxychromate (III) Na[CrF₄(H₂O)₂]

(i) Oxidation state of the central metal ion : +2 (i.e) Mn²⁺
(ii) Co-ordination number : 6
(iii) Nature of ligand: CN^- (Negative ligand)
(iv) Magnetic property: Paramagnetic nature
(v) Electronic configuration: 

(vi) Oxidation state: +2 (or) Mn²⁺ of central metal ion

Tetrahedral complexes do not exhibit geometrical isomerism. Because the relative position of donor atoms of ligand the unidentate Iigands (donor atom) attached to the central atom are same with respect to each other.

a) potassiumhexacyanidoferrate(II) - Potassiumhexacyanidoferrate(II) - K₄[Fe(CN)₆]
b) Pentacarbonyliron(0) - [Fe(CO)₅]
c) Pentaamminenitrito −kNcobalt(III)ion - [Co(NH₃)₅(NO₂)]²⁺
d) Hexaamminecobalt(III) Sulphate  - [CO(NH₃)₆](SO₄)₃
e) Sodiumtetrafluoridodihydroxidochromate(III)  - Na₂[CrF₄(OH)₂]

Metal carbonyls are classified in two different ways as described below Classification based on the number of metal atoms present.
a. Mononuclear carbonyls
These compounds contain only one metal atom. For example, [Ni(CO)₄] - nickel tetracarbonyl is tetrahedral, [Fe(CO)₅] - Iron pentacarbonyl is trigonal bipyramidal, and [Cr(CO)₆] - Chromium hexacarbonyl is octahedral.
b. Polynuclear carbonyls
Metallic carbonyls containing two or more metal atoms are called polynuclear carbonyls. Polynuclear metal carbonyls may be Homonuclear [Co₂(CO)₈], [Mn₂(CO)₁₀], [Fe₃ (CO)₁₂] or heteronuclear [MnCo(CO)₉], [MnRe(CO)₁₀] etc.

Bonding in metal carbonyls:
(i) In metal carbonyls, the bond between metal atom and the carbonyl ligand consists of two components.
(ii) The first component is an electron pair donation from the carbon atom of carbonyl ligand into a vacant d-orbital of central metal atom.
(iii) This electron pair donation forms \(M\overset { \sigma \ bond }{ \longleftarrow } \text {CO sigma bond}\)
(iv) This sigma bond formation increases the electron density in metal d orbitals and makes the metal electron rich.
(v) In order to compensate for this increased electron density, a filled metal d-orbital interacts with the empty \({ \pi }^{ \bigstar }\) orbital on the carbonyl ligand and transfers the added electron density back to the ligand.
(vi) This second component is called \(\pi\)-back bonding.
(vii) Thus in metal carbonyls, electron density moves from ligand to metal through sigma bonding and from metal to ligand through pi bonding, this synergic effect accounts for strong M⇽CO bond in metal carbonyls.
(viii) This phenomenon is shown diagrammatically as follows.

(a) coordination isomers
(b) no isomerism ( different molecular formula)
(c)⬅NCS; ⬅SCN coordinating atom differs : linkage isomers

If we perform a qualitative analysis to identify the constituent ions present in both the compounds, Mohr's salt answers the presence of Fe²⁺, NH₄^+, and SO₄^2- ions, whereas the potassium ferrithiocyanate will not answer Fe³⁺ and SCN ions. We can infer that the double salts loose their identity and dissociate into their constituent simple ions in solutions, whereas the complex ion in coordination compound, does not loose its identity and never dissociate to give simple ions.

a) Both assertion and reason are true and the reason is the correct explanation of the assertion.

a) Both assertion and reason are true and the reason is the correct explanation of the assertion.

b) I^- < Br^- < SCN^- < Cl^- < S^2- < F < OH^-