pH is a measure of how acidic or basic a solution is by looking at hydrogen ion concentration. A neutral solution occurs when the concentrations of H+ and OH− are equal. In pure water at room temperature, both ions are 1×10−7 M, so pH = -log10(1×10−7) = 7. That makes the solution neutral, meaning it is neither acidic nor basic. If the pH were less than 7, there would be more H+ and the solution would be acidic; if greater than 7, more OH− and it would be basic. (Note: neutrality is defined at standard room temperature; at other temperatures the exact pH of neutral water can shift, but the idea of equal concentrations defining neutrality remains.)

Recognize common oxyanions by their central atom and formula. The phosphate ion is the one with phosphorus surrounded by four oxygens, giving the formula PO4^3- and an overall -3 charge. This combination—phosphorus + four oxygens with a -3 charge—distinguishes it from the others: sulfate has sulfur with four oxygens and a -2 charge (SO4^2-), carbonate has carbon with three oxygens (CO3^2-), and nitrate has nitrogen with three oxygens and a -1 charge (NO3^-). So PO4^3- is the phosphate ion.

Ksp is the equilibrium constant for the dissolution of a sparingly soluble salt. When a solid dissolves, it establishes an equilibrium with its ions in solution: the solid → the ions. The solubility product is defined as the product of the activities of the ions in solution at that equilibrium. For dilute solutions, activities are well approximated by concentrations, so Ksp ≈ [M^+][X^−] for a 1:1 salt, or the appropriate product for other stoichiometries (and it depends only on temperature). This means Ksp describes how saturated the solution is with respect to that salt at a given temperature. It is not a rate constant for precipitation, nor is it simply the total amount that can dissolve (solubility), though it is related: higher Ksp generally indicates greater solubility for salts with that stoichiometry. Temperature can change Ksp, reflecting how solubility shifts with heat. So the statement that best defines Ksp is that it is the equilibrium constant for the dissolution process of a sparingly soluble salt.

A macro covalent lattice refers to a solid where covalent bonds extend throughout the entire crystal, creating a giant three→dimensional network. In such a structure every atom bonds to several neighbors in all directions, so there are no discrete molecules inside the solid. Because breaking this lattice means breaking many strong covalent bonds, these materials have very high melting points and are exceptionally hard and insoluble. Diamond is a classic example, with each carbon forming bonds to four others in a rigid framework. This contrasts with ionic lattices, which are held together by electrostatic forces between ions; metallic lattices, which consist of metal cations in a sea of delocalized electrons; and simple covalent lattices that don’t form the same extended network throughout the crystal. Hence, the term macro covalent lattice best describes substances like diamond and other giant covalent networks.