Both technicians are partially correct.
Tech A is correct that when disconnecting the battery, the negative terminal should be disconnected first. This is a standard safety precaution to prevent any accidental short circuits or sparks that could occur if the positive terminal were disconnected first. By disconnecting the negative terminal first, any accidental contact with metal tools or other conductive materials will not create a circuit.
Tech B is also partially correct that baking soda and water can remove lead oxide from battery terminals. Lead oxide can form on the terminals of a battery over time, reducing its performance and causing problems with starting and charging. Mixing baking soda with water to create a solution can help to neutralize the acidic lead oxide and make it easier to clean off the terminals. However, it's important to follow the appropriate safety precautions when handling batteries, including wearing gloves and eye protection and avoiding contact with any spilled battery acid or electrolyte solution.
In summary, both Tech A and Tech B are correct, but only in part. It's important to follow the appropriate safety guidelines and protocols when working with batteries to prevent injury or damage to the vehicle.