Option 1 states that magnetic field is a quantity that has direction and magnitude. This is correct. Magnetic field is a vector quantity, which means it has both direction and magnitude. Its direction is indicated by the orientation of the field lines, and its magnitude is measured in units of teslas.

Option 2 states that magnetic field lines are closed curves. This is correct. Magnetic field lines form closed loops around a magnet or a current-carrying wire. They always form closed curves and never end or start.

Option 3 states that magnetic field lines are open curves. This statement is incorrect. Magnetic field lines are always closed curves and do not have any open ends. They form continuous loops and never break or terminate.

Option 4 states that no two magnetic field lines are found to cross each other. This is correct. Magnetic field lines do not intersect or cross each other. If they were to intersect, it would indicate conflicting field directions at that point, which is not possible. The absence of crossings ensures the uniqueness of the magnetic field at any given point.

In summary, the correct statement regarding magnetic field is option 3, which states that magnetic field lines are open curves.