When MU is zero, TU is diminishes.

No, I do not agree with this statement.

Units of consumption
Total Utility (T.U)
Marginal Utility(M.U)
1
2
3
4
5
6
7
10
18
24
28
30
30
28
10
8
6
4
2
0
-2
         
ii. The schedule shows that with every increase in the units of Consumption, the total utility is increasing. It reaches Maximum with the 5th& 6th unit and remains the same, but with 7th unit the total utility decreases from 30-28.
         
iii. The Marginal Utility can be derived from total utility. It is observed the Marginal Utility is falling continuously. It reaches zero and then become negative.
         

iv. Thus, The Marginal Utility is Zero when total utility is Maximum and Marginal utility is negative when total utility is falling.