Assertion (A) : More and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the environment.

Reason (R) : Modern day lifestyle and a protected environment in early life has resulted in lowering the immunity.

The correct option is: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

Step-by-step Explanation:

1. Analysis of Assertion (A):
Assertion (A) states that more and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the environment. This is a well-documented medical and environmental fact. The high concentration of pollutants, dust, pollen, and other environmental allergens in urban metropolitan areas, combined with decreased exposure to natural soil and diverse microbes, makes urban children highly sensitive to their surroundings. Hence, Assertion (A) is true.

2. Analysis of Reason (R):
Reason (R) states that modern-day lifestyle and a protected environment in early life have resulted in lowering the immunity. This refers to the scientific concept known as the "Hygiene Hypothesis." According to this hypothesis, extremely clean and protected environments in early childhood limit exposure to various microbes and infectious agents. This lack of exposure prevents the immune system from developing tolerance and learning how to distinguish between harmful pathogens and harmless environmental substances. Consequently, the immune system becomes hypersensitive, leading to a higher prevalence of autoimmune and allergic disorders. Hence, Reason (R) is true.

3. Evaluating the Connection:
Since a protected modern lifestyle lowers early-life immunity development (Reason), children living in clean, urban homes in metro cities become hyper-sensitive to external environmental triggers, which directly causes them to suffer more from allergies and asthma (Assertion). Therefore, Reason (R) is the correct explanation for Assertion (A).