'Stability of a crystal is reflected in the magnitude of its melting points'. Comment. Collect melting points of solid water,ethyl alcohol,diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?

(N/A) The stability of a crystal is directly related to the magnitude of its melting point. $A$ higher melting point indicates stronger intermolecular forces of attraction,which leads to greater stability of the crystal lattice.
The melting points of the given substances are:
$1$. Solid water: $273 \ K$
$2$. Ethyl alcohol: $158.8 \ K$
$3$. Diethyl ether: $156.85 \ K$
$4$. Methane: $89.34 \ K$
Conclusion: Based on the melting point values,the intermolecular forces are strongest in solid water due to hydrogen bonding and weakest in methane due to weak London dispersion forces.