The correct answer is: A. ±2 mm.
A chain is a series of links connected together in a line. The links are typically made of metal, but can also be made of other materials such as plastic or wood. Chains are used for a variety of purposes, including lifting heavy objects, transporting goods, and securing objects.
The maximum tolerance in a chain is the amount of variation that is allowed in the length of the chain. This tolerance is typically specified in millimeters. A tolerance of ±2 mm means that the actual length of the chain can be 2 mm longer or shorter than the specified length.
The tolerance in a chain is important because it affects the accuracy of the chain. A chain with a large tolerance may not be able to be used for precise applications.
The other options are incorrect because they do not represent the maximum tolerance in a 20 m chain.