True or False: The normal breathing air concentration for oxygen is between 19.5% to 23.5%.

Answer

The correct answer is True. According to standard safety and occupational health guidelines (such as OSHA), normal ambient air contains approximately 20.9% oxygen. The accepted safe concentration range for breathing air in working environments is typically between 19.5% and 23.5%. Concentrations below 19.5% are considered oxygen-deficient, while concentrations above 23.5% create a severe fire hazard.