Indian National Ambient Air Quality standards stipulate the maximum permissible limit of the annual mean concentration of PM2.5 to be:

Correct option is C

The National Ambient Air Quality Standards (NAAQS) in India specify that the annual mean concentration of PM2.5 (fine particulate matter with a diameter of 2.5 microns or less) should not exceed 40 µg/m³. This standard is set to protect human health, as PM2.5 is associated with respiratory and cardiovascular problems.
Information Booster:
1. PM2.5 particles can penetrate deep into the lungs and are linked to health issues such as asthma, lung disease, and heart problems.
2. India’s NAAQS are established to regulate pollutants like PM2.5, PM10, NO₂, SO₂, and others to ensure cleaner air.
3. The World Health Organization (WHO) sets stricter guidelines, recommending much lower PM2.5 levels.