At atmospheric pressure and very low temperature, water crystallises to

Intercepts of a plane in crystal is given by $a, b / 2,3 c$ in a simple cubic unit cell. The miller indices are

A cubic structure is formed where atoms of element $X$ are occupied at corner of cube and also at face centers. Atoms of element $Y$ are present at body center and at the edge centers. If all the atoms are removed along a plane passing through the middle of the cube (bisecting the four edges), the formula will become

A compound can crystallise in two forms $\alpha$ and $\beta$ which are fcc and bcc, respectively. The $\alpha$-form has side length of 2 pm and the $\beta$-form has side length of 4 pm . The ratio of their density $\frac{\rho_\alpha}{\rho_\beta}$ is