Fill in the blank. The character table for a C3v molecule, such as PCl3, lists three symmetry labels: A1, A2, and E. The A1 mode transforms z, z2, and x2 + y2. This means that the A1 mode is ________________.

MCQs on the various aspects of inorganic complexes, their physical and chemical properties, and the practical applications that these complexes can have in industrial, analytical, and medicinal chemistry.