Question

what is the main goal of the investigation as described in the document? to test the durability of lab equipment to identify unknown metals using flame tests to create new chemical solutions to measure the temperature of flames

Explanation:

Flame tests are a common method in chemistry to identify unknown metals based on the characteristic colors they produce when heated in a flame. The other options seem less related to the general context suggested by the presence of the flame - test option. However, without the actual document, this is a speculative answer.

Answer:

There is no information about which document is referred to, so it's impossible to determine the correct answer. If we assume this is a chemistry - related investigation based on the options:
If the document is about chemical analysis of metals, the answer could be "To identify unknown metals using flame tests".