**3. Incorrect. The answer is true
not false.** A
∩ B means the intersection of sets A and B. This new set contains all
elements which belong to both A and B. Looking at the periodic table for
transition elements (A has a blue border and B is highlighted in yellow.), it
is easy to see that Cu is in both sets.

If there were no intersection, both sets would not have elements in
common. In that case, both sets would be called 'disjoint' sets. The
intersection of both sets gives an *empty
set* (Ř). Graphically, the Venn diagram is:

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