Final answer:
The b) presence of hydroxide ions (OH-) in a chemical formula signifies that the substance is a base. Bases release hydroxyl ions into solution or accept hydrogen ions to reduce acidity. Hydrogen ions (H+) or low pH values indicate acids, hence are not used to identify a base from its chemical formula.
Step-by-step explanation:
An easy way to identify a base from its chemical formula is by the b) presence of hydroxide ions (OH-).
Bases are substances that can release hydroxyl ions (OH-) in solution, or accept hydrogen ions (H+) already present in the solution, which combine with the hydrogen ions to form water, thereby reducing the solution's acidity.
For example, a chemical formula that contains OH- indicates a base, such as NaOH (sodium hydroxide).
Also, a solution with a pH higher than 7 is generally considered a base, as it has a lower concentration of hydrogen ions compared to pure water which has a pH of 7.
Conversely, the presence of hydrogen ions (H+) indicates an acid, and so does a low pH value.
Thus, identifying a base from the other options given in the question, the presence of hydrogen ions (a) or a low pH value (d), which are indicative of acids, and a high pH value (c), which is a result of a base being present rather than a way to identify it from its chemical formula, is incorrect.