Question

As shown in the figure, the water contact angles of surfaces A and B are $\theta_A$ and $\theta_B$, respectively. Based on the figure, which of the following statements given below is TRUE?
\includegraphics[width=0.5\linewidth]{image16.png}

• A. Surface A is hydrophilic and surface B is hydrophobic
• B. Surface A is hydrophobic and surface B is hydrophilic
• C. Both surfaces are hydrophilic
• D. Both surfaces are hydrophobic

Hint:

A smaller contact angle indicates better wetting (hydrophilic); a larger contact angle indicates poor wetting (hydrophobic).

Answer 1

The Correct Option is A

The contact angle of a water droplet on a surface determines whether the surface is hydrophilic or hydrophobic.
A surface is considered:
- Hydrophilic if the contact angle $\theta < 90^\circ$ (water spreads more, droplet flattens)
- Hydrophobic if the contact angle $\theta > 90^\circ$ (water beads up, droplet is more spherical)
From the figure:
- On Surface A, the droplet is flat and spread out. This indicates a small contact angle $\theta_A < 90^\circ$, meaning Surface A is hydrophilic.
- On Surface B, the droplet is almost spherical. This indicates a large contact angle $\theta_B > 90^\circ$, meaning Surface B is hydrophobic.
Thus, Surface A is hydrophilic and Surface B is hydrophobic.