Step 1: Understanding the Concept:
The free $-NH_{2}$ group in aniline is strongly activating and ortho/para directing. However, the nitration reaction conditions vastly alter its directing nature.
Step 2: Key Formula or Approach:
Analyze the effect of a strongly acidic nitrating mixture (conc. $HNO_3$ and conc. $H_2SO_4$) on the basic amino group during electrophilic aromatic substitution.
Step 3: Detailed Explanation:
In the presence of the strong acid used for nitration, the highly basic amino group of aniline gets protonated to form the anilinium ion ($C_{6}H_{5}NH_{3}^{+}$).
The $-NH_{3}^{+}$ group is a strongly deactivating group. Because it has a full positive charge directly attached to the benzene ring, it withdraws electron density strongly via the inductive effect ($-I$ effect) and does not possess lone pairs for resonance donation. As a result, it acts as a meta-directing group.
Therefore, a significant amount (about $47%$) of the meta isomer is formed alongside the expected para ($51%$) and ortho ($2%$) products.
Step 4: Final Answer:
The formation of the meta product is due to the presence of the meta-directing anilinium ion in the acidic medium.