(i) Ethylamine is soluble in water whereas aniline is insoluble.

• Step 1 (Concept Identification): [0.5 Mark] Ethylamine ($C_2H_5NH_2$) contains a small alkyl group which is hydrophobic, allowing the polar $-NH_2$ group to form effective hydrogen bonds with water molecules.
• Step 2 (Comparative Analysis): [0.5 Mark] In aniline ($C_6H_5NH_2$), the large hydrophobic phenyl group ($C_6H_5-$) dominates the molecule, significantly hindering the extent of hydrogen bonding with water, rendering it insoluble.

(ii) Amino group is o- and p-directing, but aniline on nitration gives m-nitroaniline.

• Step 1 (Reaction Environment): [0.5 Mark] Nitration is carried out in a strongly acidic medium using concentrated $HNO_3$ and $H_2SO_4$.
• Step 2 (Chemical Deduction): [0.5 Mark] In this acidic medium, the lone pair on the nitrogen atom of aniline is protonated to form the anilinium ion ($C_6H_5NH_3^+$). The $-NH_3^+$ group is strongly electron-withdrawing and meta-directing, leading to the formation of $m$-nitroaniline.

(iii) Amines behave as nucleophiles.

• Step 1 (Structural Basis): [0.5 Mark] The nitrogen atom in amines possesses a lone pair of electrons.
• Step 2 (Mechanism): [0.5 Mark] Due to the presence of this lone pair, amines can donate electrons to electron-deficient species (electrophiles), which is the fundamental definition of a nucleophile.

💡 EL10 Concept Insight:

Think of the lone pair on nitrogen like a "spare key" that amines can lend to other molecules; because they are always ready to share this key, they act as nucleophiles. However, if you "lock" that key by adding acid (like in the nitration of aniline), the molecule changes its behavior and stops being a friendly donor, which is why the directing power shifts!