If A,B,C are mutually perpendicular, show that Cx(AxB)=0 is the converse true?

A x B is defined as being mutually perpendicular to A and B both.

Since C is also mutually perpendicular to both A and B thus C x (A x B) = 0

yes the converse is true in the sense that C is mutually perpendicular to A and B but it does not mean that A and B are also perpendicular to each other

there can be any angle between them.