Answer is: (3) NaCl(s).
1) mercury (Hg) is liquid metal.
2) water (H₂O) is liquid molecule.
3) sodim chloride (NaCl) is crystaline solid compound.
4) methane (CH₄) is gaseous molecule.
In solid, molecules are closely packed, stiff and do not changes of shape or volume. Crystal structure is ordered arrangement of atoms, ions or molecules.
