Calculate the concentration of the solution in units of g/dm3:
10.0 g of sodium chloride dissolved in 2.00 dm3 of water

5 g/dm³ is the correct answer

Explanation:

Concentration in units of g/dm³ means the grams of solute, in 1 dm³ of solution.

We can make a rule of three:

In 2 dm³ of solution we have 10 g of NaCl

Therefore, 1 dm³ of solution we would have (1dm³ . 10g) / 2dm³ = 5g

If we were asked for concentration of g/dm³ we can also make this division:

10 g / 2dm³ = 5g/dm³