Use the grams to moles first. The molar mass of sodium is 22.99g, so 10/22.99 ≈ 0.43 moles. The use moles to atoms conversions. 0.43 x (6.022 x 10^23), which would be about 2.62 x 10^23 atoms in 10g of sodium.
The weight will decrease because more solute (osmosis) on the outside.
Decrease and Outside is the answer
