Respuesta :

Answer:

8 gm

Explanation:

NaOH molar weight = 22.989   + 15.999 + 1.008 = 39.996 gm

.5 M would contain 1/2 of this per liter = 19.998 gm

now you only want 400/1000 of a liter =   7.9992 gm ~ 8gm