Question

Angle of contact of water on an oily surface is :

• A. Acute
• B. Obtuse
• C. ${90}^{\circ }$
• D. $0^{\circ }$

Answer 1

The correct option is B Obtuse

Water will tend to repel from the oily surface, hence it will have a tendency to bead up.

Hence, the oily surface will be hydrophobic to water. Angle of contact for water molecules on the oily surface will be obtuse $(\theta >{90}^{\circ })$.

The figure below shows, the angle of contact $\theta <{90}^{\circ }$ for a surface attracting water molecules (hydrophilic) and angle of contact $\theta >{90}^{\circ }$ for a surface repelling water molecule (hydrophobic)