The correct option is C 4 in a cup
To distribute the laddus equally in cups such that none are left out, the number of laddus in a cup should be a factor of 18.
Factors of 18: 1, 2, 3, 6, 18
We can clearly see that 4 is not a factor of 18.
Hence, 4 laddus cannot be distributed in a cup such that none are left out.