Answer:
A) 0.50 M 
Step-by-step explanation:
The computation of the number of molarity of the NaOH is given below:
As we know that 
Molarity = Moles ÷ liters
where
Moles is 20
And, the liters is 40
So, the molarity is 
= 20 ÷ 40
= 0.50 M
hence, the molarity of the NaOH solution is 0.50 M
Therefore the A option is correct