Chemistry MCQs for NEET — Practice Questions with Answers

An outer orbital complex involves the use of the outer d orbitals in bonding. Among the given options, $ [Ni(NH_3)_6]^{2+} $ is an outer orbital complex. This is because Nickel in this complex uses its 4s and 4p orbitals for bonding, rather than the inner 3d orbitals.

$ [Co(NH_3)_6]Cl_3 $ is a low-spin complex due to the presence of strong field ligand NH3. In this case, all electrons are paired up, leading to a magnetic moment of zero. Therefore, the correct answer is zero.

In $Fe(CO)_5$, the bonding involves both sigma ($ ext{σ}$) and pi ($ ext{π}$) characters. The carbon monoxide ligand donates a pair of electrons to form a sigma bond with the iron atom. Additionally, the filled d-orbitals of iron back-donate electrons into the empty π*-orbitals of the CO ligand, forming a pi bond. This synergic bonding results in a bond that has both sigma and pi characters.

According to Werner’s theory, coordination compounds have two types of valencies: primary and secondary. The primary valency corresponds to the oxidation state of the metal and can be ionized. The secondary valency corresponds to the coordination number of the metal and involves coordinate bonds with ligands, which typically cannot be ionized.

Ligands in a complex salt can be either ions or molecules linked by coordinate (dative covalent) bonds to a central metal atom or ion. This means that ligands can be anions, cations, or neutral molecules, as long as they donate a pair of electrons to the metal center to form a coordinate bond.

According to Lewis, a ligand is a species that donates a pair of electrons to a metal ion to form a coordination complex. Since ligands donate electron pairs, they are considered Lewis bases. Hence, they are basic in nature.

The coordination number refers to the number of ligand donor atoms bonded to the central metal ion. In the complex $[Co(en)_2Br_2]Cl_2$, 'en' stands for ethylenediamine, which is a bidentate ligand (each 'en' contributes 2 donor atoms). So, there are 2 'en' ligands contributing 4 donor atoms and 2 bromide ions each contributing 1 donor atom, making a total of 6 donor atoms. Therefore, the coordination number of cobalt in this complex is 6.

A hexadentate ligand can form six bonds with a central metal ion. Ethylenediaminetetraacetic acid (EDTA) is an example of a hexadentate ligand as it can donate six pairs of electrons to a metal ion. Therefore, ethylene diammine tetra acetate ion (EDTA) is the correct example of a hexadentate ligand.

The primary valency of a metal ion in a coordination compound is its oxidation state. In $K_2[Ni(CN)_4]$, the complex ion is $[Ni(CN)_4]^{2-}$ and potassium (K) has a charge of +1. Therefore, the primary valency of nickel (Ni) must be +2 to balance the charge of the complex ion.