**Core Concept**
The patient is experiencing postpartum hemorrhage (PPH) due to uterine atony, which is a common complication after cesarean section (LSCS). Uterine atony refers to the failure of the uterus to contract effectively after delivery, leading to excessive bleeding.

**Why the Correct Answer is Right**
The patient's symptoms, such as pallor, abdominal distension, tachycardia, and a significant drop in hemoglobin, suggest severe PPH. The pelvic exam revealing mild PPH further confirms the diagnosis. The next step in management is to administer uterotonic agents, specifically oxytocin, to stimulate uterine contractions and control bleeding. Oxytocin works by binding to oxytocin receptors on the smooth muscle cells of the uterus, causing contraction and vasoconstriction, which helps to reduce bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering a blood transfusion would be a secondary measure to stabilize the patient's blood pressure and replace lost blood, but it is not the immediate next step in managing uterine atony.
**Option B:** Performing an immediate laparotomy would be an invasive and aggressive approach, usually reserved for cases of severe PPH that do not respond to medical management.
**Option C:** Administering ergot alkaloids, such as ergometrine, could be considered, but oxytocin is generally the first-line treatment for uterine atony due to its efficacy and safety profile.

**Clinical Pearl / High-Yield Fact**
In cases of PPH, it's essential to remember the "4 Ts": Tone (uterotonic agents), Tamponade (balloon tamponade), Tissue (surgical exploration), and Tranfusion (blood transfusion). Each of these measures should be considered in sequence to manage PPH effectively.

**Correct Answer:** C. Administer oxytocin to stimulate uterine contractions and control bleeding.