Which of the following quantities is the same for one mole of Br2(l) and one mole of He(g)?
Number of molecules
Number of atoms
Total mass of the particles
Volume occupied at s.t.p
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Discussions (10)
The correct answer is: A. Number of molecules
Explanation:
Let’s examine each option for 1 mole of Br₂(l) and 1 mole of He(g):
A. Number of molecules 
1 mole of any substance contains Avogadro’s number of molecules (≈
6.022
×
10
23
6.022×10
23
).
So, 1 mole of Br₂(l) =
6.022
×
10
23
6.022×10
23
Br₂ molecules
1 mole of He(g) =
6.022
×
10
23
6.022×10
23
He atoms
So the number of molecules is the same (1 mole = 1 mole)
B. Number of atoms 
Br₂ has 2 atoms per molecule, so 1 mole of Br₂ has 2 × Avogadro’s number =
1.204
×
10
24
1.204×10
24
atoms
He is monoatomic → just
6.022
×
10
23
6.022×10
23
atoms
So not the same
C. Total mass of the particles
Molar mass of Br₂ ≈ 160 g/mol
Molar mass of He ≈ 4 g/mol
So, their total mass is not the same
D. Volume occupied at s.t.p
This only applies to gases, and Br₂ is a liquid at s.t.p.
So, volumes can’t be directly compared under same gas laws
Final Answer: A. Number of molecules
avogadroo's hypothesis states that equal volume of gases at same conditions contain equal number of molecules.
Both one mole of
Br2(𝑙) and one mole of He(𝑔)
He(g) has the same number of molecules (in the case of helium, each atom is considered a molecule), making choice A the correct answer
The answer is A, let’s note that Bromine is in liquid state so the gas molar volume at stp does not apply here.
