Correct Answer - Option 3 : -14.5 °C
Pv = Partial pressure of water vapour at temperature = 20°C
Now \(\frac{{{P_v}}}{{{P_s}}} = 0.05\) (given)
∴ Form table,
Ps= 2.34 kPa
∴ Pv = 0.05 × 2.34= 0.117 kPa.
Now we have to find that temperature at which Pv become saturated pressure by interpolation method.
\(T = - 15 + \left[ {\frac{{\left( { - 10 + 15} \right)}}{{\left( {0.26 - 0.10} \right)}} \times \left( {0.117 - 0.10} \right)} \right]\)
= -15 + 0.5312
= - 14.468°C
= - 14.5°C