**Core Concept**
Burns are classified based on their depth, which affects their treatment, prognosis, and potential complications. The depth of a burn is determined by its effect on the skin layers.

**Why the Correct Answer is Right**
In partial-thickness burns, also known as second-degree burns, the epidermis and some of the dermis are affected. However, the burn is not deep enough to destroy the entire dermis. In this scenario, the patient's lower limbs and genitalia are charred, indicating that the burn is not superficial but has penetrated beyond the epidermis. The presence of charring suggests that the burn is deep enough to affect the deeper dermal layers, making it a third-degree burn. However, the fact that the genitalia are also involved indicates that the burn is not a third-degree burn, as these areas are typically spared in third-degree burns due to the presence of thicker skin and better vascular supply.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because partial-thickness burns typically do not involve charring and are typically not as deep as third-degree burns.
**Option B:** This option is incorrect because third-degree burns typically spare the genitalia due to the thicker skin and better vascular supply.
**Option C:** This option is incorrect because fourth-degree burns involve deeper structures such as muscle, bone, and nerve, which are not indicated in this scenario.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the depth of a burn is not always immediately apparent and may require debridement and histopathological examination to confirm.

**Correct Answer: B. Third-degree burns typically involve deeper structures such as muscle, bone, and nerve, but in this scenario, the genitalia are also involved, making it a fourth-degree burn.