The correct option is A 87.5 mL
M1V1=M2V2
Where,
M1⇒ Molarity of the initial solution = 3.5 M
V1⇒ Volume of the initial solution = 50 mL
M2⇒ Molarity of the resultant solution i.e. after dilution = 2 M
V2⇒ Volume of the resultant solution
3.5×50=2×V2
V2=3.5×502=87.5 mL
Therefore, the initial solution must be diluted to 87.5 mL.