Which one of the following statement(s) is/are incorrect?
    (i)    The ratio of load on wheel to contact area or area of imprint is called as contact pressure.
    (ii)    The ratio of load on wheel to contact pressure is called as rigidity factor.
    (iii)   The value of rigidity factor is more than three for an average tyre pressure of 7 kg/cm2.
    (iv)    Rigidity factor depends upon the degree of tension developed in walls of tyres.