The Brainliest Answer!
The no. of elements in {b} is the no. of elements in A. 
Since, it is one-one fucntion.
One-One function is that function whose domain and range have equal no. of elements as each element of A is connected to only one element of B. Elements of A has only one image in B
2 5 2
Explain it that how u come to this point?
please mark it BRAINLIEST i need it.