For \([V(\text{H}_2\text{O})_6]^{3+}:\)
Vanadium (V) has an atomic number of 23, with an electronic configuration of \([ \text{Ar} ] 3d^3 4s^2\). \(\text{V}^{3+}\) configuration: \([ \text{Ar} ] 3d^2\). Number of unpaired \(d\)-electrons: 2 (even number).
For \([Cr(\text{H}_2\text{O})_6]^{2+}:\)
Chromium (Cr) has an atomic number of 24, with an electronic configuration of \([ \text{Ar} ] 3d^5 4s^1\). \(\text{Cr}^{2+}\) configuration: \([ \text{Ar} ] 3d^4\). Number of unpaired \(d\)-electrons: 4 (even number).
For \([Fe(\text{H}_2\text{O})_6]^{3+}:\)
Iron (Fe) has an atomic number of 26, with an electronic configuration of \([ \text{Ar} ] 3d^6 4s^2\). \(\text{Fe}^{3+}\) configuration: \([ \text{Ar} ] 3d^5\). Number of unpaired \(d\)-electrons: 5 (odd number).
For \([Ni(\text{H}_2\text{O})_6]^{3+}:\)
Nickel (Ni) has an atomic number of 28, with an electronic configuration of \([ \text{Ar} ] 3d^8 4s^2\). \(\text{Ni}^{3+}\) configuration: \([ \text{Ar} ] 3d^7\). Number of unpaired \(d\)-electrons: 3 (odd number).
For \([Cu(\text{H}_2\text{O})_6]^{2+}:\)
Copper (Cu) has an atomic number of 29, with an electronic configuration of \([ \text{Ar} ] 3d^{10} 4s^1\). \(\text{Cu}^{2+}\) configuration: \([ \text{Ar} ] 3d^9\). Number of unpaired \(d\)-electrons: 1 (odd number).
From the analysis above, only \([V(\text{H}_2\text{O})_6]^{3+}\) and \([Cr(\text{H}_2\text{O})_6]^{2+}\) have an even number of unpaired \(d\)-electrons.
The number of complexes with an even number of unpaired \(d\)-electrons is 2, corresponding to Option (1).
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 : \(A_2 \rightleftharpoons 2A\)
A black body is at a temperature of 2880 K. The energy of radiation emitted by this body with wavelength between 499 nm and 500 nm is U1, between 999 nm and 1000 nm is U2 and between 1499 nm and 1500 nm is U3. The Wien's constant, b = 2.88×106 nm-K. Then,