The upper and lower concentrations of a vapor that will produce a flame at a given pressure and temperature are:

The upper and lower concentrations of a vapor that will produce a flame at a given pressure and temperature are:

• A. flash points.
• B. vapor densities.
• C. flammable and explosive limits.
• D. burning points.

Answer: (C)

The concept being tested is the range of vapor concentrations in air that can burn, known as the flammable limits (also called explosive limits). This range has a lower limit and an upper limit. The lower limit is the minimum vapor concentration that can sustain ignition, while the upper limit is the maximum concentration that can still ignite. Between these two values, a flame can be started and kept going if an ignition source is present at the given pressure and temperature. These limits shift with changes in pressure and temperature, so at higher temperatures the range often widens because vapors form more readily and ignition becomes easier. For context, below the lower limit the mixture is too lean to ignite, and above the upper limit it’s too rich to burn. The term flash point isn’t about a concentration range at a specific pressure/temperature—it’s the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture. Vapor density relates to how heavy the vapor is compared with air, not the burning range. Burning point isn’t a standard term used for this concept.

The concept being tested is the range of vapor concentrations in air that can burn, known as the flammable limits (also called explosive limits). This range has a lower limit and an upper limit. The lower limit is the minimum vapor concentration that can sustain ignition, while the upper limit is the maximum concentration that can still ignite. Between these two values, a flame can be started and kept going if an ignition source is present at the given pressure and temperature. These limits shift with changes in pressure and temperature, so at higher temperatures the range often widens because vapors form more readily and ignition becomes easier.

For context, below the lower limit the mixture is too lean to ignite, and above the upper limit it’s too rich to burn. The term flash point isn’t about a concentration range at a specific pressure/temperature—it’s the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture. Vapor density relates to how heavy the vapor is compared with air, not the burning range. Burning point isn’t a standard term used for this concept.