Chemistry MCQs for NEET — Practice Questions with Answers

Lesser is the oxidation state of Cr in oxide, more is the basic nature.

Mn²⁺ and Fe³⁺both have 5 unpaired electrons. So, they have same magnetic moment

In lanthanoid only Promethium (Pm) 61 is radioactive

In lanthenoid series, as we move from left to right then basic nature of hydroxide decrease.

Sc³⁺ has no unpaird electron. Hence it is colourless.

Actinoids show different oxidation states such as +2, +3, +4, +5, +6 and +7. However +3 oxidation state is most common among all the actinoids.

The wide range of oxidation states of actinoids is attributed to the fact that the 5f, 6d and 7s energy levels are of comparable energies.

Therefore, all these three subshells can participate.

A charge-transfer complex (CT complex) or electron-donor-acceptor complex is an association of two or more molecules, or of different parts of one large molecule, in which a fraction of electronic charge is transferred between the molecular entities. The resulting electrostatic attraction provides a stabilizing force for the molecular complex. The source molecule from which the charge is transferred is called the electron donor and the receiving species is called the electron acceptor.

The nature of the attraction in a charge-transfer complex is not a stable chemical bond, and is thus much weaker than covalent forces. Many such complexes can undergo an electronic transition into an excited electronic state. The excitation energy of this transition occurs very frequently in the visible region of the electromagnetic spectrum, which produces the characteristic intense color for these complexes. These optical absorption bands are often referred to as charge-transfer bands (CT bands). Optical spectroscopy is a powerful technique to characterize charge-transfer bands.

Charge-transfer complexes exist in many types of molecules, inorganic as well as organic, and in solids, liquids, and solutions. A well-known example is the complex formed by iodine when combined with starch, which exhibits an intense blue charge-transfer band.

In inorganic chemistry, most charge-transfer complexes involve electron transfer between metal atoms and ligands. The charge-transfer bands of transition metal complexes result from shift of charge density between molecular orbitals (MO) that are predominantly metal in character and those that are predominantly ligand in character. If the transfer occurs from the MO with ligand-like character to the metal-like one, the complex is called a ligand-to-metal charge-transfer (LMCT) complex. If the electronic charge shifts from the MO with metal-like character to the ligand-like one, the complex is called a metal-to-ligand charge-transfer (MLCT) complex. Thus, a MLCT results in oxidation of the metal center, whereas a LMCT results in the reduction of the metal center. Resonance Raman spectroscopy^[1] is also a powerful technique to assign and characterize charge-transfer bands in these complexes.

In the dichromate ion (Cr2O7^2-), there are 6 equivalent Cr-O bonds. The dichromate ion has a tetrahedral geometry with two chromium atoms and seven oxygen atoms. The Cr-O bonds are equivalent due to the delocalization of electrons within the ion.

[Ar]4s²3d⁶ $\stackrel{-3{\mathrm{e}}^{-}}{\to }$[Ar]3d⁵

          [X]

Hence , the atomic number of [X] is 26

K₃[Fe(CN)₅(H₂O)] has zero unpaired electron and it has zero magnetic moment

Fe ⁺² is having d⁶ configuration,CN being stronger ligand so thy will pair up electrons to form d²sp³ hybridization