_______ of electrolyte indicates the state of charge of the battery

The correct answer is: D. specific gravity

The specific gravity of the electrolyte is a measure of its density relative to water. The specific gravity of a fully charged battery is between 1.260 and 1.280. As the battery discharges, the specific gravity decreases. A specific gravity of less than 1.220 indicates that the battery is discharged and needs to be recharged.

The other options are incorrect because:

• Color: The color of the electrolyte is not a reliable indicator of the state of charge of the battery. The color can vary depending on the type of battery and the age of the battery.
• Mass: The mass of the battery does not change significantly as the battery discharges.
• Viscosity: The viscosity of the electrolyte is a measure of its resistance to flow. The viscosity of the electrolyte does not change significantly as the battery discharges.