Question

The atom that has the largest atomic radius among the following:

• A. Zn
• B. Cu
• C. Ni
• D. Co

Answer 1

The correct option is A Zn

The atomic radius decreases along the period but in d- block elements across the period shielding effect also take place.
Due to the balancing effect of shielding and increase in $Z_{eff}$, atomic radius is almost same for Co, Ni and Cu.
s- subshell has more shielding effect and Copper having an exceptional electronic configuration has only 1 electron in s subshell whereas zinc has 2 electrons, so more electronic repulsion.
Because of this Zn has largest atomic radius among the options.