No. 5 - This is a regular polyomino, more precisely, a pentomino (all 12 pieces that can be constructed out of 5 squares)
in a rectangular surface of 6 x 10.
Confirming Tenyo there exist 2339 distinct solutions for this puzzle! That is quite a bit more than I expected with only 12 pieces!
My Free download version Pentomino solver for Windows does also find 2339 solutions.

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