Calculate the concentration in % (m/m) of a solution containing 30.0g of mgcl2 dissolved in 270.0g of h20

A 11.75%

B 10.0 %

C 8.34 %

D 7.41 %

E 15.0 %

As the question tells you, you need to use the formula

% mass = mass of solute / mass of solution x 100

mass solute = 30.0 g

mass of solution = 30.0 + 270.0 = 300.0 g

% mass = 30.0 / 300.0 x 100 = 10%

answer is B