Basic Terms Questions in English

(D) $1$. $A$ ligand is an ion or molecule that binds to a central metal atom to form a coordination complex.
$2$. $NH_3$ (Ammonia) is a neutral ligand.
$3$. $CH_3NH_2$ (Methylamine) is a neutral ligand.
$4$. $N_2H_5^+$ (Hydrazinium) is a positively charged ligand.
$5$. $NO_3^-$ (Nitrate) is a negatively charged ligand (anionic ligand).
$6$. Therefore, the correct option is $D$.

(A) The co-ordination number of a metal atom in a complex is defined as the number of ligand donor atoms to which the metal is directly bonded. Therefore, the correct option is $A$.

(B) Step $1$: Analyze the ligands in each complex.
$(a)$ $[Ni(CN)_4]^{2-}$: The ligand is $CN^-$, which is a monodentate ligand.
$(b)$ $[AlF_6]^{3-}$: The ligand is $F^-$, which is a monodentate ligand.
$(c)$ $[Cu(NH_3)_4]^{2+}$: The ligand is $NH_3$, which is a monodentate ligand.
$(d)$ $[Al(C_2O_4)_3]^{3-}$: The ligand is $C_2O_4^{2-}$ (oxalate), which is a bidentate ligand.
Step $2$: Count the complexes containing only monodentate ligands. Complexes $(a)$, $(b)$, and $(c)$ contain only monodentate ligands. Complex $(d)$ contains a bidentate ligand.
Step $3$: The total number of such complexes is $3$.

(A) $1$. Identify the ligands in each complex:
- In $[Fe(CO)_5]$, the ligand is $CO$ (carbonyl), which is a neutral ligand.
- In $[Fe(CN)_6]^{4-}$, the ligand is $CN^-$ (cyano), which is an anionic ligand.
- In $[Co(C_2O_4)_3]^{3-}$, the ligand is $C_2O_4^{2-}$ (oxalato), which is an anionic ligand.
- In $[Co(NO_2)_6]^{3-}$, the ligand is $NO_2^-$ (nitro), which is an anionic ligand.
$2$. Since $CO$ is a neutral molecule, $[Fe(CO)_5]$ contains a neutral ligand.
$3$. Therefore, the correct option is $A$.

(C) $1$. The complex is $[Co(en)_3]^{3+}$, where $Co^{3+}$ is the central metal ion.
$2$. The ligand $en$ stands for ethylenediamine $(NH_2CH_2CH_2NH_2)$, which is a bidentate ligand.
$3$. $A$ bidentate ligand donates two lone pairs of electrons to the central metal ion.
$4$. The coordination number is calculated as: $\text{Number of ligands} \times \text{denticity} = 3 \times 2 = 6$.
$5$. Therefore, the coordination number of the central metal ion is $6$.

(B) $1$. $A$ heteroleptic complex is a coordination complex in which the central metal atom or ion is bonded to more than one type of donor group (ligand).
$2$. In $[Fe(CO)_5]$, all ligands are $CO$.
$3$. In $[Co(NH_3)_3(NO_2)_3]$, the central metal $Co^{3+}$ is bonded to two different types of ligands: $NH_3$ and $NO_2^-$.
$4$. In $[Cu(NH_3)_4]^{2+}$, all ligands are $NH_3$.
$5$. In $[Ni(CN)_4]^{2-}$, all ligands are $CN^-$.
$6$. Therefore, $[Co(NH_3)_3(NO_2)_3]$ is the heteroleptic complex.

(D) complex is neutral if the net charge on the coordination entity is zero.
$(1)$ $K_3[Fe(CN)_5NO]$: The coordination entity is $[Fe(CN)_5NO]^{3-}$, which is charged.
$(2)$ $[Zn(NH_3)_4]^{2+}$: This is a cationic complex with a charge of $+2$.
$(3)$ $[Co(NH_3)_5Cl]^{2+}$: This is a cationic complex with a charge of $+2$.
$(4)$ $[Ni(CO)_4]$: The oxidation state of $Ni$ is $0$ and $CO$ is a neutral ligand. The net charge is $0 + 4(0) = 0$. Thus, it is a neutral complex.

(C) The complex $[Co(NH_3)_6]Cl_2$ dissociates in solution as follows:
$[Co(NH_3)_6]Cl_2 \rightarrow [Co(NH_3)_6]^{2+} + 2Cl^-$
Number of $[Co(NH_3)_6]^{2+}$ ions = $1$
Number of $Cl^-$ ions = $2$
Total number of ions per molecule = $1 + 2 = 3$.