In the density formula ρ = PM/RT, what does M represent?

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Multiple Choice

In the density formula ρ = PM/RT, what does M represent?

Explanation:
M stands for the molar mass of the gas. This density relation comes from starting with the ideal gas law PV = nRT and using ρ = m/V with m = nM. Since n = m/M, substitute into PV = nRT to get PV = (ρV)RT/M, then solve for ρ to obtain ρ = PM/RT. That shows why M is the molar mass: it ties the total mass to the amount of substance in moles. It’s not the density itself, not the universal gas constant, and not a temperature scale.

M stands for the molar mass of the gas. This density relation comes from starting with the ideal gas law PV = nRT and using ρ = m/V with m = nM. Since n = m/M, substitute into PV = nRT to get PV = (ρV)RT/M, then solve for ρ to obtain ρ = PM/RT. That shows why M is the molar mass: it ties the total mass to the amount of substance in moles. It’s not the density itself, not the universal gas constant, and not a temperature scale.

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