. Which of the following has the least value of coefficient of friction?

The correct option is A

Rolling friction

Explanation for correct answer: option(A)

1. The frictional coefficient describes as the ratio of the force of friction between two bodies and the normal force pressing them together.
2. Coefficient of static friction ${\mu }_s=\frac{f_s}{N}$; $f_s=$static frictional force, $N=$normal reaction force
3. Coefficient of sliding or kinetic friction ${\mu }_k=\frac{f_k}{N}$; $f_k=$kinetic frictional force, $N=$normal reaction force
4. Coefficient of rolling friction,${\mu }_r=\frac{f_r}{N}$ ; $f_r=$rolling frictional force, $N=$ normal reaction force
5. The values of µs and µk depend on the nature of both the surfaces in contact.${\mu }_s>{\mu }_k>{\mu }_r$

Hence, Rolling friction has the least value of coefficient of friction.