29.2%(w/w) HCI stock solution has a density of 1.25g mL^-1. The molecular weight of HCI is 36.5g mol^-1. The volume (mL) of stock solution required to prepare a 200mL solution of 0.4M HCI is

Density of HCl=1.25 g mL solution-1 Weight of 100 mL solution = 125g for a 29.2% (W/W)
HCl solution, weight $=\frac{125}{100}\times 29.2=36.5\mathrm{gm}$ soin 100mL solution, moles of HCl
36.5/36.5 = 1 moles so molarity of HCl=10M using M₁V₁=M₂V₂ volume required V₂x10=200x0.4 V₂=8mL.