# Chemistry Class 11 NCERT Solutions: Chapter 5 States of Matter Part 6

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Q: 18. 2.9 g of a gas at 95 ° C occupied the same volume as 0.184 g of dihydrogen at 17 °C, at the same pressure. What is the molar mass of the gas?

Volume (V) occupied by dihydrogen is given by,

Let M be the molar of the unknown gas. Volume (V) occupied by the unknown gas can be calculated as:

According to the question,

Hence, the molar mass of the gas is .

Q: 19. A mixtures of dihydrogen and Dioxygen at one bar pressure contain by weight of dihydrogen. Calculate the partial pressure of dihydrogen.

Let the weight of dihydrogen be 20 g and the weight of Dioxygen be 80 g.

Then, the number of moles of dihydrogen, and the number of moles

Of Dioxygen,

Given,

Total pressure of the mixture,

Then, partial pressure of dihydrogen,

Hence, the partial pressure of dihydrogen is

Q: 20. What would be the SI unit for the quantity

The SI unit for pressure, p is

The

The SI unit for the number of moles is mol.

Therefore, the SI unit for quantity is given by,

Q: 21. In terms of Charles’ law explain why is the lowest possible temperature.

Charles’ law states that constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.