Question

without friction It wouldn't be possible to tie a knot in give reason

Answer 1

Frictional force is due to the roughness of surfaces.
Now when you tie a knot due to the roughness of the surfaces of the material used the knot gets tied and until an unbalanced force is not applied the knot is tied.
But if the surfaces of the material to be tied is very smooth i.e. no frictional force between them they will oppose to get tied in the form of knot and will maintain their shape but since there is frictional force a material can be tied because frictional force overcomes the tendency of an object to maintain its shape.