Convection this is because convection is bull movement of molecules between fluids
Answer: HBr has the lowest rate of effusion at a given temperature.
Explanation: The effusion rate usually increases with increase in temperature because the kinetic energy of the gaseous molecules increases. But it was not true for gases having heavier mass. This was explained by Graham's Law.
Graham's Law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular weight.

We are given different gases with different Molecular masses. The gas having larger Molecular mass will have the lowest rate of effusion.
Mol. Mass of
= 80 g/mol
Mol. Mass of
= 16 g/mol
Mol. Mass of
= 17 g/mol
Mol. Mass of HBr = 81 g/mol
Mol. Mass of HCl = 36 g/mol
As, Mol. mass of HBr is the highest, so its rate of effusion will be the lowest.
91.4 grams
91.4 grams of kcl in grams must be added to 500 ml of a 0. 15 m kcl solution to produce a 0. 40 m solution.
C = mol/volume
2.45M=mol/0.5L
2.45M⋅0.5L = mol
mol = 1.225
Convert no. of moles to grams using the atomic mass of K + Cl
1.225mol * 
mol=1.225
=1.225 mol . 
=1.225 . 74.6
=91.4g
therefore, 91.4 grams of kcl in grams must be added to 500 ml of a 0. 15 m kcl solution to produce a 0. 40 m solution.
What is 1 molar solution?
In order to create a 1 molar (M) solution, 1.0 Gram Molecular Weight of the chemical must be dissolved in 1 liter of water.
58.44 g make up a 1M solution of NaCl.
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