(a), because inverse of a function is basically its mirror image in the line y=x. So only way mirror images coincide is if they are at 0 distance from the mirror i.e they lie on y=x
My bad, they may not necessarily intersect there. Counter example would be f(x)=-x^3 and g(x)=-(x)^1/3, which intersect at (-1,1) and (1,-1) so (c) is correct. For the points to lie on y=x the function has to be strictly increasing.
According to your solution they are not intersection point, P(α, β) and Q(β,α) intersect only if they are same point's coordinate because they are intersection point of f and inv f. So α = β and slope of a single point is undefined.
If P(a,b) and Q(c,d) are two different intersection point of f and inv f then should lie on y = x. and
slope of PQ will be 1.
Do lnx and e^x intersect each-other? how and where ?