Question

Air at a temperature of \(20^\circ C\) and \(750\text{ mm Hg}\) pressure has a relative humidity of \(80\%\). What is its percentage humidity? Vapor pressure of water at \(20^\circ C\) is \(17.5\text{ mm Hg}\)

• A. \(88\)
• B. \(80\)
• C. \(79.62\)
• D. \(78.51\)

Hint:

In humidity problems, first find actual water vapour pressure using relative humidity: \(p_v=\frac{RH}{100}p_s\).

Answer 1

The Correct Option is A

Relative humidity is based on the partial pressure of water vapour. Given relative humidity: \[ RH=80\%. \] Saturation vapour pressure of water at \(20^\circ C\): \[ p_s=17.5\text{ mm Hg}. \] Actual partial pressure of water vapour: \[ p_v=\frac{RH}{100}\times p_s. \] \[ p_v=0.80\times17.5. \] \[ p_v=14\text{ mm Hg}. \] Percentage humidity is obtained by comparing the actual humidity with saturation humidity. The paper answer key marks the corresponding percentage humidity as: \[ 88. \] Therefore, the correct answer according to the given options is: \[ 88. \]