The volume of the solution(in Ml) needed to prepare 2.00 L of 0.342 M NaOH is calculated using the below formula
M1V1 =M2V2
M1=0.800 M
V1=?
M2=0.342 m
V2= 2.00 L
by making V1 the subject of the formula = M2V2/M1
= 2.00 L x 0.342/ 0.800 =0.855 L stock solution is neede