Final answer:
The molecule or ion with a trigonal planar shape is SO₃.
Step-by-step explanation:
The molecule or ion that has a trigonal planar shape is option B) SO₃. In the SO₃ molecule, sulfur is surrounded by three oxygen atoms, forming a trigonal planar shape with bond angles of 120°. The Lewis structure of SO₃ shows that sulfur has three electron groups with no lone pairs, leading to a trigonal planar molecular shape.