* A used immediately: While some film developing chemicals are time-sensitive, many have a usable shelf life. Using them immediately isn't always necessary.

* C uncovered metal pans: This is absolutely incorrect. Film developing chemicals are often reactive and can corrode metal. Leaving them uncovered exposes them to air, which can lead to oxidation and spoilage, making them less effective.

Here's why airtight containers are crucial:

* Prevent Oxidation: Air contains oxygen, which can react with developing chemicals, degrading their effectiveness.

* Prevent Evaporation: Some chemicals are volatile and can evaporate if left open. This weakens the solution and affects development results.

* Maintain Consistency: Airtight containers help keep the chemicals from absorbing moisture or other contaminants, ensuring consistency in development.

Important Note: Always follow the manufacturer's instructions for specific chemical handling, storage, and disposal.