Redox reactions play a pivotal role in chemistry and biology. The values of standard redox potential $$\left(\mathrm{E}^{\circ}\right)$$ of two half-cell reactions decide which way the reaction is expected to proceed. A simple example is a Daniel cell in which zinc goes into solution and copper gets deposited. Given below are a set of half-cell reactions (acidic medium) along with their $$\mathrm{E}^{\circ}$$ (V with respect to normal hydrogen electrode) values. Using this data obtain the correct explanations.

$$\begin{array}{ll} \mathrm{I}_{2}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{I}^{-} & \mathrm{E}^{\mathrm{o}}=0.54 \\ \mathrm{Cl}_{2}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{Cl}^{-} & \mathrm{E}^{\mathrm{o}}=1.36 \\ \mathrm{Mn}^{3+}+\mathrm{e}^{-} \rightarrow \mathrm{Mn}^{2+} & \mathrm{E}^{\mathrm{o}}=1.50 \\ \mathrm{Fe}^{3+}+\mathrm{e}^{-} \rightarrow \mathrm{Fe}^{2+} & \mathrm{E}^{\mathrm{o}}=0.77 \\ \mathrm{O}_{2}+4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_{2} \mathrm{O} & \mathrm{E}^{\mathrm{o}}=1.23 \end{array}$$

Sodium fusion extract, obtained from aniline, on treatment with iron (II) sulphate and $$\mathrm{H}_{2} \mathrm{SO}_{4}$$ in presence of air gives a Prussian blue precipitate. The blue colour is due to the formation of

Riemer-Tiemann reaction introduces an aldehyde group, on to the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

Which one of the following reagents is used in the above reaction?

Riemer-Tiemann reaction introduces an aldehyde group, on to the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

The electrophile in this reaction is :

Riemer-Tiemann reaction introduces an aldehyde group, on to the aromatic ring of phenol, ortho to the hydroxyl group. This reaction involves electrophilic aromatic substitution. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

The structure of the intermediate I is