c) A calcium atom is larger than a zinc atom.
Ca (1s2)(2s2,2p6)(3s2,3p6) (3d0) (4s2) Z* = 20 (10 · 1.00 + 8 · 0.85 + 1 · 0.35) = 2.85
Zn (1s2)(2s2,2p6)(3s2,3p6) (3d10) (4s2) Z* = 30 (10 · 1.00 + 18 · 0.85 + 1 · 0.35) = 4.35
The electrons in the 4s level experience a greater effective nuclear charge in Zn than in Ca. The electrons in Zn are therefore attracted to the nucleus to a larger extent than the electrons in calcium. So the atomic radius is smaller. In general the Z* increases more slowly across a d block compared to a p block. The reason is the electrons being added in the dblock are inside the ns electrons, while for the p block the electrons are not inside the ns electrons.