Answer : The number of atoms of helium atom remain in the balloon are,

Explanation : Given,
Moles of helium present in balloon = 6.0 mole
Moles of helium escape from balloon = 4.0 mole
First we have to calculate the moles of helium remains in the balloon.
Moles of helium remains in the balloon = Moles of helium present in balloon - Moles of helium escape from balloon
Moles of helium remains in the balloon = 6.0 - 4.0 = 2.0 mole
Now we have to calculate the number of helium atoms remain in the balloon.
As, 1 mole of helium atom remain in the balloon contains
number of helium atoms.
So, 2.0 mole of helium atom remain in the balloon contains
number of helium atoms.
Therefore, the number of helium atom remain in the balloon are,
