What is the coordination number of the $hcp$ crystal lattice?

In a body-centered cubic $(BCC)$ unit cell,how many metal atoms surround the metal atom located at the center of the cell?

What is the value of the radius ratio for an ionic crystal having a coordination number of $6$?

If three elements $X$,$Y$ and $Z$ crystallise in a $ccp$ lattice with $X$ atoms at the corners,$Y$ atoms at the cube centre and $Z$ atoms at the edges centre,the formula of the compound will be

What are two types of crystal structures shown by ice at different pressures?

For an ionic crystal with the general formula $AX$,the coordination number is $6$. What is the radius ratio range?