Which of the following are true-
In cardinal approach,
a) When TU is rising at an increasing rate, MU also rises .
b) When TU is rising at decreasing rate, MU falls.
c) MU falls due to Law of Diminishing Marginal Utility.
d) When TU is maximum MU is 0.

a, b, c and d

The relationship between TU and MU can be explained as follows: 

• When MU increases, TU increases at an increasing rate.
• When MU decreases, TU increases but at a diminishing rate.
• When MU is zero, TU is at its maximum.
• When MU is negative, TU starts declining.