Answer: Option B. -> False
:
B
Friction depends on the nature of surfaces in contact and the force with which the surfaces are pressed against each other. It doesn't depend on the area of contact. Thus, frictional force will not change even if the given objectis dragged along the top surface instead of the bottom.

Answer: Option C. -> Ice
:
C
When a body is slidalong a horizontal surface,frictional force opposes its motion. This means that the body will travel to the maximum distance on the surface having least friction. Among the givensurfaces, ice has the least friction and the ball will travel the farthest on ice.

Answer: Option A. -> Interlocking of irregularities present on the surfaces
:
A
Friction is caused by interlocking of irregularities present on the surfaces in contact. Rough surfaces have larger irregularities while smoother surfaces have lesser irregularities. Hence, rough surfaces offer more friction as compared to smooth surfaces.Even surfaces that appear smoothhave numerous minute irregularities present on them.

Answer: Option B. -> False
:
B
Sincerolling friction is lessthan sliding friction,it is easier to roll a body than to slide (drag) it along a surface. Thus, the given statement is false.

Answer: Option D. -> Grease
:
D
The substances which when applied between two surfaces reduce friction between themare known as lubricants. They help in reducing heat generation, andwear and tear in machines. Grease is a commonly used lubricantwhichis used in machines to reduce friction.

Answer: Option C. -> Both the statements are correct.
:
C
Friction is caused by the interlocking of irregularities present on thesurfaces in contact. Rough surfaces have a largenumber of irregularities and generally have more friction.
Thisfrictional force increases if the two surfaces are pressed harder. For example, one can easily draga mat when nobody is sitting on it. However, dragging the same mat becomes quite difficult when a person is sitting on it. Thus, both the statements are correct.

Answer: Option A. -> True
:
A
The given statement is true. Ball bearings are used in many machines to utilize rolling friction instead of sliding friction between moving parts. Rolling friction is preferred as it is less in magnitude than sliding friction and henceimproves efficiency of the machine.

Answer: Option D. -> Towards left
:
D
Frictional force always opposes relative motion between two surfaces in contact. As the book is being pushed towards right, friction will act towards left to oppose this impending motion.

Answer: Option C. -> Frictional force
:
C
While walking, we apply a force on ground in backward direction. The ground, in turn, applies a force on us in forward direction. This force is basically the frictional force which opposesslipping between our foot and ground.

Answer: Option A. -> Static friction > sliding friction > rolling friction.
:
A
When a body starts sliding, the contact points on its surfacedo not get enough time to lock into the other surface. So, sliding friction is slightly smaller than maximum static friction. It is always easier to roll than to slide a body over another.So, rolling friction is further smaller than sliding friction. Hencethe correct order is: static friction > sliding friction > rolling friction.