Question

Why anticlockwise motion is positive and clockiwse motion is negative

Answer 1

It follows from the general convention which is handed down to us from generations and is universally accepted. Another reason could be that: A charged particle be it an electron or a proton would move along a circular path in a uniform magnetic field. However, the direction of motion would depend upon the magnitude of charge as positive charge would move in an anticlockwise orbit while a negative charge would move in a clockwise orbit.