Which of the following statements are TRUE about frictional force? i. it is always a disadvantage ii. it is sometimes a disadvantage iii. it always exist wh...

The statement that is true about frictional force is that it is sometimes very useful, which is represented by option ii, iv only. Frictional force is the force that opposes motion between two surfaces that are in contact with each other. While it can be a disadvantage in certain situations, such as when it causes wear and tear on machinery or creates heat, it can also be very useful. For example, friction allows us to walk without slipping, provides the necessary grip for car tires to adhere to the road, and allows us to write with a pen or pencil. Without frictional force, it would be challenging to perform many daily tasks that we take for granted. Therefore, statement ii and iv are true, as frictional force is sometimes useful, and it exists where there is relative motion of two bodies in contact. Statement i is false, as frictional force is not always a disadvantage, and statement iii is partly true, as frictional force does exist where there is relative motion of two bodies in contact, but it can also exist even if there is no relative motion.