Final answer:
The density of dry air decreases when the temperature increases from standard temperature to 100°C, assuming the pressure remains constant at 1.00 atm. This is in accordance with the ideal gas law and Charles's law.
Step-by-step explanation:
Density of Dry Air at Different Temperatures
The density of dry air at standard temperature and pressure (STP) is given as 1.29 g/L. When temperature changes and pressure remains constant, the density of air changes accordingly. According to Charles's law, volume is directly proportional to temperature when pressure is constant, and according to the ideal gas law (PV = nRT), if the volume of a gas increases, the density (density = mass/volume) decreases. At 100°C or 373 K (Kelvin), assuming pressure remains at 1.00 atm, the density of dry air decreases compared to its density at standard temperature due to the increase in temperature.
To further understand, let's consider the given example of a hot air balloon. In a hot air balloon calculation, it is assumed that the pressure inside and outside the balloon is the same, and the density is only affected by the temperature changes, similar to the scenario described for air at 100°C.
The ideal gas law can be manipulated to show that density is directly proportional to pressure and inversely proportional to temperature. Therefore, if we increase the temperature while keeping the pressure constant, the density must decrease. Hence, the correct choice in the scenario given (air at 100°C and 1.00 atm pressure) is: A. Decreases.