Question

For tap water and clean glass, the angle of contact is

• A. $0^o$
• B. ${90}^o$
  
• C. ${140}^o$
  
• D. $8^o$
  

Answer 1

The correct option is D $8^o$

The angle of contact between pure water and glass is found to be $0^0$ as both cohesive forces and adhesive forces are equal. But due to presence of ions in tap water the angle of contact is acute from $8^0$ to ${18}^0$.