**Core Concept**
Achalasia cardia is a rare swallowing disorder characterized by the failure of the lower esophageal sphincter (LES) to relax, leading to difficulty in passing food into the stomach. This condition is often associated with esophageal dysmotility and a significant risk of esophageal carcinoma.

**Why the Correct Answer is Right**
The correct answer, **B. Males are affected more than the females**, is incorrect because achalasia cardia actually affects females more than males. The exact cause of this gender disparity is unknown, but it may be related to hormonal influences on the esophagus. The LES failure to relax in achalasia cardia is a critical aspect of this condition, and manometry is indeed the most confirmatory investigation for diagnosing achalasia.

**Why Each Wrong Option is Incorrect**
**Option A:** The lower esophageal sphincter (LES) does indeed fail to relax normally in achalasia cardia, which is a hallmark of the condition. This failure to relax leads to difficulty in passing food into the stomach.

**Option C:** The absence of gastric air bubble is a classic sign seen on X-ray in achalasia cardia, which is a result of the LES failure to relax and the subsequent accumulation of food and air in the esophagus.

**Option D:** Manometry is indeed the most confirmatory investigation for achalasia cardia. It measures the pressure and coordination of the esophageal muscles, providing a definitive diagnosis of achalasia.

**Clinical Pearl / High-Yield Fact**
Achalasia cardia is often associated with a significant risk of esophageal carcinoma, particularly in patients who have had symptoms for more than 5 years. Regular follow-up and surveillance are essential to detect any potential malignancies early.

**✓ Correct Answer: B. Males are affected more than the females**