H+ is a positively charged hydrogen ion, which is not expected to form a crystalline structure with oppositely charged ions. The other options, H-, Mg2+, and Ca2+, are all ions that are capable of forming crystalline structures with oppositely charged ions.

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Heating an aqueous solution of borax above 62°C results in the evaporation of water molecules. Among the given options, Na2B4O7.5H2O is the correct structure for heptahydrate form of sodium tetraborate, which is formed when the solution is heated. Removing water molecules leaves behind Na2B4O7·5H2O crystals.

The states of matter of CO2 and SiO2 at room temperature differ due to their structural differences. CO2 is a molecular compound with weak intermolecular forces, while SiO2 has a rigid network covalent structure, making it solid at room temperature.

Ethyne, also known as acetylene, has a straight-line molecular structure due to its triple bond between the two carbon atoms, resulting in a linear geometry. This structure is characterized by a bond angle of 180 degrees.

When water freezes, its molecules arrange in a unique hexagonal structure that contains empty spaces. This causes the density of the solid ice to be lower than that of liquid water.

Acetone is a symmetrical ketone because it has a methyl group on both sides of the carbonyl group, resulting in a mirror-image molecular structure.

Sintered glass is a porous material created by fusing small glass particles together. Its porous structure makes it suitable for various applications. In this multiple-choice question, we are asked about the primary use of sintered glass. Among the given options, 'filtration' is the correct choice. Other options like absorption, adsorption, and sublimation can be related to sintered glass's capabilities, but filtration is its primary use, as it allows the separation of solids from liquids or gases by trapping the particles within its porous structure.

Black phosphorus is the most stable allotropic form of phosphorus, which is obtained by heating white phosphorus in the absence of air. It has a layered structure and is more stable than other allotropic forms due to its strong covalent bonds.

At constant temperature, the pressure of an ideal gas is inversely proportional to its volume. This inverse relationship results in a straight line when 1/V is plotted against pressure.