If set contains four elements and set contains five elements, then the number of one-one and onto…

Answer: (b) 0 A function from set $A$ to set $B$ can be both one-one and onto (bijective) only if the two sets have the same number of elements. Since $n(A) = 4$ and $n(B) = 5$, no mapping can be onto, so the number of one-one and onto mappings is 0.