Final answer:
The method most likely to be used is immersion, which involves placing a thermometer directly into the liquid.
Step-by-step explanation:
The method most likely to be used to measure the temperature of a liquid contained in an open vessel is immersion. This involves placing a thermometer directly into the liquid, allowing it to come into contact with the liquid and measure its temperature. By immersing the thermometer in the liquid, it provides an accurate measurement of the liquid's temperature.
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