Final answer:
The correct specific gravity range for a fully charged motive-power battery is B. 1.120 - 1.280, which indicates the density of the electrolyte and the battery's charge state.
Step-by-step explanation:
The correct specific gravity range for the electrolyte in a fully charged motive-power battery is B. 1.120 - 1.280. Specific gravity is a measure of the density of the electrolyte solution compared to the density of water. A hydrometer can be used to test specific gravity and thereby assess the state of charge of the battery's cells. In a lead-acid battery, when charged, the sulfation on the plates dissolves back into the acid making the electrolyte denser. Therefore, a higher specific gravity indicates a fully charged state.
During the charging process, it is important to avoid excessive voltage which can lead to electrolysis of water within the battery. Appropriate charging voltages take into account overvoltages necessary to drive the electrochemical reactions needed to return the battery to a fully charged state. For example, a car battery typically requires approximately 14 V to recharge efficiently despite having a nominal voltage of 12 V.