That would be evaporation.
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Answer: The given statement is true.
Explanation:
According to the Dalton's law, total pressure of a mixture of gases that do not react with each other is equal to the partial pressure exerted by each gas.
The relationship is as follows.

or, 
where,
....... = partial pressure of individual gases present in the mixture
Also, relation between partial pressure and mole fraction is as follows.

where,
= mole fraction
Thus, we can conclude that the statement Dalton's law of partial pressures states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture, is true.
50 grams or 50,000 mili grams is the mass of solute in 1000 grams of a solution having a concentration of 5 parts per million.
Explanation:
Total mass of solution = 1000 grams or 1000 ml since 1 gram = 1 ml
concentration is 5 parts per million ( 5 mg in 1000 ml solution or 0.005 gram in 1000 ml)
the formula used for parts per million:
parts per million = 
putting the values in the equation:
parts per million = 
0.005 x 1000 = mass of solute
50 grams= mass of solute
converting this into mg
50,000 mg. is the total mass of solute in 5ppm of 1000 ml solution.
Mass of Na2SO4= 514.18 grams
<h3>Further explanation</h3>
Given
423.67 g of NaCl
Required
mass of Na2SO4
Solution
Reaction
2NaCl + H2SO4 → Na2SO4 + 2HCl
mol NaCl :
= 423.67 g : 58.5 g/mol
= 7.24
From the equation, mol Na2SO4 :
= 1/2 x mol NaCl
= 1/2 x 7.24
= 3.62
Mass Na2SO4 :
= 3.62 mol x 142,04 g/mol
= 514.18 grams