Which of the following lattices has the highest packing efficiency: $(i)$ simple cubic,$(ii)$ body-centred cubic,and $(iii)$ hexagonal close-packed lattice?

An alloy of metals $A$,$B$,and $C$ is found to have $A$ constituting a $ccp$ lattice. If $B$ atoms occupy the edge centers and $C$ is present at the body center,the formula of the alloy is:

The number of octahedral and tetrahedral holes respectively present in a hexagonal close packed $(hcp)$ crystal of $X$ atoms are

In a crystal,atoms of $A$ form an $FCC$ lattice,atoms of $B$ occupy all octahedral voids,and atoms of $C$ occupy $25\%$ of the tetrahedral voids. The possible molecular formula of the compound is:

$A$ compound is formed by two elements $A$ and $B$. The element $B$ forms a cubic close-packed $(CCP)$ structure and atoms of $A$ occupy $\frac{1}{3}$ of the tetrahedral voids. If the formula of the compound is $A_x B_y$,then the value of $x+y$ is:

Vacant space in body centered cubic $(BCC)$ lattice unit cell is about (in $\%$)