the thread of mercury in a thermometer is 17cm when placed above boiling water, and 9cm when dipped in melting ice. how long would the thread of mercury become if placed in a liquid with a temperature of 75 degree celsius.

is there a method or formula for this?

Yes there is a method. Assume a linear relationship. A temperature range of 100 C (from melting ice to boiling water) moves the mercury column 17-9 = 8 mm
A 75 degree temperature is 3/4 of the way from the 0 degree mark to the 100 degree mark. That is 6 cm past the 0 C mark, or 15 cm.

If you want to use an equation, let X = distance from the bottom of the "thread" of mercury
X = a T + b is the linear relationship.
a and b are constants you must determine.
When T = 0, X = 9, so b = 9
When T = 100, X = 17, so
17 = a*100 + 9
8 = 100 a
a = 0.08 cm per degree.
X = 9 + 0.08 T

When T = 75 C, X = 9 + (75*0.8) = 15 cm

okay... but i think i know another formular which is basically the same, but thanks anyway!

Ggghhhfg

For i think the answer is 12.75cm if we go by ratio and proportion;

100℃=17cm
75℃= x
Cross multiply 75x17 =1275℃/cm
100℃
Degrees celcius will go remain with cm,then 100 into 1275 is
12.75Cm

You're welcome! There may be multiple formulas or methods to solve the problem, and it's great that you have another one in mind. The important thing is to understand the concept of linear relationships and how they can be applied to determine the length of the mercury thread in a thermometer at a specific temperature. If you have any further questions or need assistance with anything else, feel free to ask!