The correct option is D 2m2−m
Let A={a1,a2,a3,….,am}
⇒A×A=⎧⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎨⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎩(a1,a1),(a1,a2),…,(a1,am)(a2,a1),(a2,a2),…,(a2,am)....(am,a1),(am,a2),…,(am,am)⎫⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎬⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎭
n(A×A)=m2
Let us Consider elements in A×A as
1)Diagonal elements D1={(a1,a1),(a2,a2)...(am,am)}
2)Non diagonal elements D2={(a1,a2),(a2,a1),(a1,a3),(a3,a1)...(am−1,am),(am,am−1)}
n(D1)=m,n(D2)=m2−m
Now for relation to be reflexive
1) there is only one choice for diagonal elements i.e It has to be included to make relation reflexive
2) for each of m2−m non diagonal elements, there are two choices either it can be included or excluded to make relation reflexive.
∴ from principle of counting, number of reflexive relations
=1×1×...×1(m times)×2×2×...×2(m2−m times)
=2m2−m