For which ionic compound is the radius ratio $0.93$?

Platinum crystallizes in a face-centered cubic $(FCC)$ crystal with a unit cell edge length $a$. The distance between nearest neighbour atoms is

An ionic compound has a unit cell consisting of $A$ ions at the corners of a cube and $B$ ions on the centres of the faces of the cube. The empirical formula for this compound would be

The coordination number of a metal crystallising in a hexagonal close-packed $(HCP)$ structure is

What is the two-dimensional coordination number of a molecule in a square close-packed layer?

The coordination number in $hcp$ is