Question

How many grams of sucrose will be necessary to prepare 300 ml of a 5% solution of sucrose (342.0 g/mol)

Answer 1

5% what. weight/volume? weight/weight? volume/volume?
I assume you mean w/v since you want 300 mL of solution.
5% means 5 g sucrose/100 mL solution. You want 300 so
5g x (300/100) = 15g
So you need 15 g sucrose/300 mL solution.