The attraction of a complex to a magnetic field depends on the number of unpaired electrons in the complex. Let us analyze each given complex:
1.[Zn(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Zn\(^{2+}\) is \( 3d^{10} \). It has no unpaired electrons, so it is diamagnetic.
2. [Ni(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Ni\(^{2+}\) is \( 3d^8 \). In an octahedral field, this gives a \( t_{2g}^6 e_g^2 \) configuration, with 2 unpaired electrons.
3. [Co(en)\(_3\)]\(^{3+}\): The electronic configuration of Co\(^{3+}\) is \( 3d^6 \). Due to strong-field ligands (en), it undergoes pairing, resulting in a \( t_{2g}^6 e_g^0 \) configuration with no unpaired electrons. It is diamagnetic.
4. [Co(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Co\(^{2+}\) is \( 3d^7 \). In an octahedral field with weak-field ligands like water, it gives a \( t_{2g}^5 e_g^2 \) configuration with 3 unpaired electrons. Hence, [Co(H\(_2\)O)\(_6\)]\(^{2+}\) has the maximum number of unpaired electrons and will exhibit the maximum attraction to an applied magnetic field.
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)

Cobalt chloride when dissolved in water forms pink colored complex $X$ which has octahedral geometry. This solution on treating with cone $HCl$ forms deep blue complex, $\underline{Y}$ which has a $\underline{Z}$ geometry $X, Y$ and $Z$, respectively, are

What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)