**Core Concept**
β2 selective agonists are a class of medications that activate β2 adrenergic receptors, leading to bronchodilation and smooth muscle relaxation in the respiratory tract. This pharmacological effect makes them particularly useful in treating respiratory conditions characterized by bronchospasm.

**Why the Correct Answer is Right**
In asthma, β2 selective agonists, such as salbutamol and terbutaline, work by stimulating β2 adrenergic receptors in the bronchial smooth muscle, causing relaxation and dilation of the airways. This leads to an increase in airflow and a decrease in symptoms such as wheezing and shortness of breath. The β2 selectivity of these agonists minimizes the risk of systemic side effects associated with non-selective β agonists, such as tachycardia and tremors.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta 2 selective agonists are not the primary treatment for angina due to coronary insufficiency, as they do not directly address the underlying issue of reduced coronary blood flow. Instead, they may even worsen the condition by increasing myocardial oxygen demand.
**Option C:** Delayed labor is typically managed with tocolytic agents such as nifedipine or ritodrine, which work by relaxing the uterine smooth muscle. Beta 2 selective agonists are not the preferred choice for this indication due to potential risks of neonatal hypoglycemia and other complications.

**Clinical Pearl / High-Yield Fact**
Beta 2 selective agonists are a key component of asthma management, but they should be used judiciously, as repeated or high-dose use can lead to tolerance and decreased effectiveness. It's essential to monitor patients for signs of tachyphylaxis and adjust treatment plans accordingly.

**✓ Correct Answer: B. Asthama**