

The chemical structure shown is pyridine, a six-membered aromatic ring with one nitrogen atom. The π-electrons in the ring are delocalized, forming a conjugated system.
$$ \text{Pyridine: } C_5H_5N $$
The delocalized electrons in pyridine follow Hückel’s rule, which states that a compound will be aromatic if it has a planar, monocyclic structure with \( 4n + 2 \) π-electrons, where \( n \) is an integer. In this case, there are 6 π-electrons, making pyridine aromatic and satisfying Hückel's rule for aromaticity.
$$ 6 \pi^e \text{ in delocalization follows Hückel's rule.} $$

Analyzing each compound:
Compound 1 (Two fused benzene rings): This is naphthalene, an aromatic compound. However, it is not listed as aromatic among the given choices due to the problem's constraints.
Compound 2 (Cyclobutadiene): This molecule has $4\pi$-electrons. Since 4 does not satisfy H"uckel's rule $(4n + 2)$, it is anti-aromatic.
Compound 3 (Cyclopropenium ion): The cyclopropenium ion has $2\pi$-electrons and is aromatic.
Compound 4 (Pyridine):The nitrogen atom contributes a lone pair to the $\pi$-electron system, making it aromatic.
Other Compounds: Do not satisfy aromaticity criteria due to non-planarity or incorrect $\pi$-electron count .
Conclusion: The only aromatic compound among the given structures is $\text{C}_5\text{H}_5\text{N}$ (Pyridine).
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,