To analyze the properties of K$_3$[Co(CN)$_6$], let's break it down:
Oxidation state of cobalt: The overall charge on the complex is 0. Let $x$ represent the oxidation state of cobalt: \[ 3 + x - 6 = 0 \implies x = +3 \] So, Co is in the +3 oxidation state.
Electronic configuration of \(Co^{3+}\): Cobalt's ground state is [Ar] \(3d^7 4s^2\).
After losing 3 electrons, the configuration becomes \(3d^6\).
Ligand strength: CN$^-$ is a strong field ligand (SFL) as per the spectrochemical series. Strong field ligands cause significant splitting of the d-orbitals, leading to pairing of electrons in the lower energy orbitals.
Electron pairing: In the presence of CN$^-$, the 3d electrons pair as follows: \[ \text{Before pairing: } \uparrow \uparrow \uparrow \uparrow \uparrow \uparrow \] \[ \text{After pairing: } \uparrow \downarrow \uparrow \downarrow \uparrow \downarrow \] As all electrons are paired, the complex is diamagnetic.
Geometry: The coordination number is 6, and with CN$^-$ being a strong ligand, the geometry is octahedral.
Stability: CN$^-$ forms strong bonds with the metal center due to its strong field nature, making K$_3$[Co(CN)$_6$] the most stable complex among the options.
Thus, K$_3$[Co(CN)$_6$] is octahedral, diamagnetic, and the most stable.
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,