NEET Practice Questions (MCQs) with Answers & Solutions

The thermal stability of transition metal elements is influenced by the magnitude of their ionization enthalpy. Elements with higher ionization enthalpies tend to have more stable compounds because the energy required to remove an electron is greater, making it harder for the element to participate in reactions that would lead to decomposition.

The color of an aqueous solution of $[Ni(H_2O)_6]^{2+}$ is green. This is due to the d-d transitions of the nickel(II) ion in the octahedral crystal field created by the water ligands. The specific wavelengths of light absorbed and emitted result in the observed green color.

The complex ion $[Co(NH_3)_6]^{3+}$ is known to have a yellowish-orange color in its aqueous solution. This is due to the electronic transitions within the d-orbitals of the cobalt ion influenced by the ligand field created by the ammonia molecules.

$Co^{2+}$ ions typically exhibit a pink color in their hydrated form, and $Mn^{2+}$ ions are also known to be pale pink. Therefore, the correct option is $Co^{2+}$ and $Mn^{2+}$, which match the description of having a pink color.

$Ti^{3+}$ ions are known to exhibit a purple color. This is due to the specific electronic transitions within the d-orbitals of the titanium ion, which absorb certain wavelengths of light and reflect the purple color.

The color of hydrated salts is due to the d-d transitions of the metal ions in the crystal field created by the water molecules. Here are the correct matches:

1. $NiCl_2 ullet 6H_2O$ is green
2. $Co(NO_3)_2 ullet 6H_2O$ is pink
3. $FeCl_3$ is yellow
4. $CuSO_4 ullet 5H_2O$ is blue

Therefore, the correct matching is 1-d, 2-a, 3-e, 4-c.

In the contact process for the production of sulfuric acid, $V_2O_5$ (vanadium pentoxide) is used as the catalyst to convert $SO_2$ to $SO_3$. The reaction is as follows:

$$2SO_2 + O_2 ightarrow 2SO_3$$

This reaction is catalyzed by $V_2O_5$.