All three metals finish a filled d-subshell with one or two s-electrons sitting on top, so their ionization energies come down to how tightly each nucleus holds that outer electron. Silver holds its outer electron the loosest, thanks to relativistic effects and greater shielding. Zinc holds its electrons the tightest because its whole 3d\(^{10}\)4s\(^2\) arrangement is unusually stable, and copper falls in between. So the increasing order is silver, then copper, then zinc, option (A).