The correct answer is A) visual inspection of the pressure gage. The state of charge of a stored pressure type dry chemical fire extinguisher can be readily determined by visual inspection of the pressure gage. This is because the pressure gage indicates the amount of internal pressure in the extinguisher, which directly corresponds to the amount of dry chemical agent stored within the cylinder. As the extinguisher is used or loses pressure over time, the pressure gage will show a lower reading, allowing the operator to easily check the extinguisher's charge level. The other options are incorrect because they do not provide an easy or reliable way to check the state of charge. Removing the lid (B) is not a practical method, and weighing the cylinder (C) or CO2 cartridge (D) would require additional equipment and may not give an accurate assessment of the dry chemical agent level.