Answer:
[NaOH] = 0.1 Molar ... Note => the brackets around formula;i.e., "[ ]" is generally accepted in the chemistry community as concentration in Molar terms.
Step-by-step explanation:
The metathesis rxn, or double replacement rxn, equation is:
(Molarity x Volume) of acid = (Molarity x Volume) of base, or
(M·V)acid = (M·V)base => M(base) = M·V(acid)/V(base)
= 0.1M × 18.3ml / 20ml = 0.0915M(base) = 0.1M (1 sig-fig) = [NaOH]