The temperature when the mercury level is 6.5 cm above the lower mark is 26 °C.
To determine the temperature from the mercury level on a centigrade thermometer, you need to use the formula:
Temperature = (Mercury level / Distance between fixed points) * 100
In this case, the distance between the fixed points is 25cm, and the mercury level is 6.5 cm above the lower mark. Plugging these values into the formula gives:
Temperature = (6.5 cm / 25 cm) * 100 = 26 °C
So the temperature is 26 °C when the mercury level is 6.5 cm above the lower mark on a centigrade thermometer with fixed points 25 cm apart.