**Core Concept**
Congenital adrenal hyperplasia (CAH) is a group of inherited disorders that affect the adrenal glands, leading to impaired production of cortisol and aldosterone, and often resulting in the overproduction of androgens. This condition is primarily caused by mutations in genes encoding enzymes involved in the steroidogenesis pathway, specifically the 21-hydroxylase enzyme.

**Why the Correct Answer is Right**
The most common form of CAH is 21-hydroxylase deficiency, accounting for approximately 95% of cases. This deficiency leads to a buildup of precursor steroids, which are shunted towards the production of androgens, resulting in virilization of female infants and individuals with this condition. The other forms of CAH, such as 11-β hydroxylase deficiency, are significantly less common.

**Why Each Wrong Option is Incorrect**
**Option A:** Autosomal recessive disorder. This statement is correct and not the answer we are looking for, but let's explain why the other options are wrong. The rest of the options are incorrect because they are related to the wrong type of CAH or its manifestations.

**Option B:** 11-β Hydroxylase deficiency is most common. This statement is incorrect because 11-β hydroxylase deficiency is the second most common form of CAH, accounting for approximately 5% of cases, not the most common form.

**Option C:** Commonest cause of genital ambiguity at birth. This statement is incorrect because 21-hydroxylase deficiency is the most common cause of CAH, which leads to virilization of female infants and is the commonest cause of genital ambiguity at birth, not 11-β hydroxylase deficiency.

**Option D:** Hypoglycemia is seen. This statement is incorrect because hypoglycemia is not typically seen in CAH, especially in the more common forms like 21-hydroxylase deficiency. However, it can occur in the salt-wasting form of CAH due to the impaired production of aldosterone.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the diagnosis of CAH is often suspected based on clinical presentation, including ambiguous genitalia in newborns, and confirmed through hormonal and genetic testing. Early diagnosis and treatment are crucial to prevent long-term consequences such as infertility, osteoporosis, and hypertension.

**✓ Correct Answer: B. 11 - β Hydroxylase deficiency is most common.**