40% by mass urea is obtained by dissolving 190 gof urea in certain amount of water. The mass of amount of water used is

The mass of element present in the grams for every 100 g  of the total mass of the mixture is called as mass percentage. 

Given: mass percentage of urea is 40%

Mass of urea used is 190 g

Let the mass of water used be x

Mass of solution will be the sum of urea and water,

Substituting the values,

Solving for x

285 g

Therefore, 285 gof water is needed to make 40%by mass urea solution and the correct option is C.