## Core Concept
The question tests knowledge of dental anatomy, specifically the internal structure of primary molars. Primary molars have a different anatomy compared to permanent molars, including variations in the number of pulpal horns. Understanding the typical anatomy of primary teeth is crucial for pediatric dentistry.

## Why the Correct Answer is Right
The mandibular second primary molar typically has 5 pulpal horns. These correspond to the 5 cusps often seen on the tooth, although the number of cusps can vary. The pulpal horns are directly related to the cusps of the tooth, extending into each cusp. This anatomy is significant for procedures like pulpotomies, where the goal is to remove infected pulp while preserving the vitality of the remaining pulpal tissue.

## Why Each Wrong Option is Incorrect
**Option A:** This option suggests fewer pulpal horns than typically found in a mandibular second primary molar.
**Option B:** This option suggests an incorrect number of pulpal horns, not aligning with the typical anatomy.
**Option C:** This option might seem plausible but does not accurately reflect the commonly accepted number of pulpal horns for this tooth.
**Option D:** This option suggests more pulpal horns than typically associated with the mandibular second primary molar.

## Clinical Pearl / High-Yield Fact
A key point to remember is that primary molars have a higher pulp-to-tooth volume ratio compared to permanent teeth. This makes procedures like pulpotomies more feasible in pediatric dentistry. Knowing the typical number of pulpal horns in each primary tooth is essential for effective and safe dental treatment.

## Correct Answer: D. 5