What should soldiers do after placing iodine tablets in their canteen?

Waiting 25-30 minutes after placing iodine tablets in the canteen before consuming the water is the correct practice. This waiting period allows sufficient time for the iodine to effectively disinfect the water. Iodine works as a purifying agent, killing bacteria and viruses to make the water safe for drinking. If consumed too soon, the water may still harbor pathogens, posing a risk to health.

The other choices suggest shorter waiting times that do not provide the necessary duration for iodine to fully sanitize the water, compromising its safety. Inverting the canteen or immediately sealing it without allowing the iodine sufficient time to act would also fail to ensure proper disinfection, potentially leading to illness if the water is contaminated. Thus, adhering to the recommended 25-30 minute time frame is crucial for ensuring that the water is treated effectively.