Step-by-step explanation:
A 300-ml of 0.100M HCl solution contains
0.100M HCl = (0.100 mol HCl/L) × (0.300 L)
----> 0.03 mol HCl
So we need to find the volume of 12M HCl solution that contains 0.03 mol HCl
0.03 mol HCL = (12 mol HCl/1 L)×V
or
V = (1 L × 0.03 mol HCl)/(12 mol HCl)
= 0.0025 L
= 2.5 ml
So you need 2.5 ml of 12M HCl to be diluted with distilled water to 300 ml in order to get a 0.100M HCl solution.