Chemistry MCQs for NEET — Practice Questions with Answers

Transition elements are known to exhibit variable valencies due to the involvement of (n-1)d and ns electrons in bonding. This is a characteristic property of transition metals.

The element with atomic number 56 is Barium (Ba), which belongs to the group of alkaline earth metals in the periodic table.

German silver is an alloy composed primarily of copper, zinc, and nickel. It does not contain silver, hence the percentage proportion of silver in german silver is 0%.

Both Lanthanoids and Actinides exhibit variable oxidation states. This is due to the fact that their electrons can occupy f-orbitals, which allows them to exhibit multiple oxidation states. This property is more pronounced in Actinides compared to Lanthanoids.

The magnetic moment ( ext{in BM}) is calculated using the formula $ ext{μ}_{ ext{eff}} = ext{√}(n(n+2))$ where n is the number of unpaired electrons. For $Mn^{2+}$ (d^5), $Cr^{2+}$ (d^4), and $V^{2+}$ (d^3), the number of unpaired electrons are 5, 4, and 3 respectively. Thus, the order is $Mn^{2+} > Cr^{2+} > V^{2+}$.

The stability of $Gd^{3+}$ ion is due to its half-filled 4f orbital, which provides extra stability according to Hund's rule. A half-filled 4f orbital configuration means that it has exactly 7 electrons, which is a stable arrangement due to maximum spin multiplicity.

The ion $Ti^{4+}$ cannot show d-d transitions because it has an empty d-orbital (3d^0 configuration). D-d transitions require electrons in the d-orbitals to move between different d-orbital energy levels, but since $Ti^{4+}$ has no electrons in its d-orbitals, such transitions cannot occur.

The electronic configuration $(n-1)d^5 ns^2$ can show the highest oxidation state. This is because elements with this configuration have a half-filled d-subshell, which is relatively stable and can lose more electrons to achieve a higher oxidation state. An example is manganese (Mn) with configuration $3d^5 4s^2$, which can exhibit an oxidation state of +7.

Potassium dichromate ($K_2Cr_2O_7$) is commonly used to oxidize ferrous ions (Fe^2+) to ferric ions (Fe^3+) in an acidic medium. It acts as a strong oxidizing agent in various chemical reactions.

Cerium oxide ($CeO_2$) is commonly used as a pigment due to its excellent properties such as high stability and resistance to heat. It is often used in ceramics and glass to provide a yellow color.