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1 a5 mol of helium.

b1 kg of helium has 1000/4 moles whereas 1 kg of uranium has 1000/238 moles. Hence helium has more atoms.

c1 mol of each element has the same number of atoms, but the mole of uranium weighs more. So an atom of uranium is heavier.

2 P=W A=ρ V g A=ρ A h g A=ρ h g.

So, the cylinder with the greater height exerts the greater pressure.

3Draw a vertical line that will intersect the two straight lines. These points have the same

temperature. The blue line has higher pressure and so smaller volume by the Boyle–Mariotte law.

Alternatively from P V = n R T we get P=n R V T so the gradient of a P–T graph is n R V. The blue curve has larger gradient and so smaller volume.

4b is the correct answer.

a is a correct statement, but it does not explain why the pressure increases.

c is wrong since T = constant.

5From U=3 2 n R T, helium, having more moles (10 versus 1 for argon), has higher internal energy.