In which of the following close-packed structures, the radii r of their spheres respectively is correctly represented?

\(\text{hcp, ccp : }\frac{a}{2\sqrt{2}}, \frac{a}{2\sqrt{2}}\)

The correct answer is option 2. \(\text{hcp, ccp : }\frac{a}{2\sqrt{2}}, \frac{a}{2\sqrt{2}}\).

In Hexagonal close packing (hcp),

\(4r = \sqrt{2}a\)

or, \(r \frac{\sqrt{2}a}{4}\)

or, \(r = \frac{a}{2\sqrt{2}}\)

In Cubic close packing

\(4r = \sqrt{2}a\)

or, \(r \frac{\sqrt{2}a}{4}\)

or, \(r = \frac{a}{2\sqrt{2}}\)

Thus the answer is option 2. \(\text{hcp, ccp : }\frac{a}{2\sqrt{2}}, \frac{a}{2\sqrt{2}}\)