Option (A) is the correct answer because the statement is factually incorrect. Robert Brown discovered the nucleus, not the cell. The cell was first discovered by Robert Hooke. The other options are correct statements: Schleiden and Schwann formulated the cell theory, Virchow explained that cells are formed from pre-existing cells (which is supported by Question 2 in the context stating new cells generate from pre-existing cells), and a unicellular organism carries out its life activities within a single cell.