The correct answer is - to measure confirmed or fixed temperature.
Explanation:
When the liquid of the flask was being heated, temperature rises of the liquid and when thermometer is being place in flask to measure the temperature of liquid of the flask the liquid present in thermometer is also start to rise.
The rise in the liquid is due to increse of the temperature due to flow of the heat from high temperature to low temperature are until the tempearture become equal. So, the when the liquid stop rising it means both are on same temperature and this is the measure ment of the liquid of the flask.
