Answer:
D. 2.5 dm3
Explanation:
Alright, first off, you gotta find how many moles Sodium Hydroxide (NaOH) has.
20.0g NaOH x (1 mol / 40.0g NaOh (got amount from Periodic Table))
Basically, it's 20.0g / 40.0g, which gives 0.5 mol since the grams cancel each other. Then we know the pyramid (mol / M x L) so...
0.5 mol x 0.20 M = 2.5 dm3