If set \(A\) contains 4 elements and the set \(B\) contains 5 elements, then the number of onto mappings from \(A\) to \(B\) is

0

Since number elements in the set \(A\) is 4 and number of elements in the set \(B\) is 5, which is greater than 4.

Mapping can be done to only 4 elements of the set \(B\) as there has to be unique image from elements of set \(A\) to set \(B\).

Which means the Range can have only 4 elements out of 5. Hence no onto mapping is possible as in onto mapping all elements in the set \(B\) needs to have pre-image.