The correct option is C 900 mL
∙ Flask A has 450 mL of potion.
∙ Flask B has almost double the volume of potion in flask A.
∙ So, the estimated volume of potion in flask B = 2 × 450 mL = 900 mL
∙ Therefore, the estimated volume of potion in flask B is 900 mL.
Hence, option C is correct.