Question

How many liters of 0.85 M HCI solution would react completely with 3.5 moles Ca (OH)2?

Answer 1

Ca(OH)2+2HCL=CaCl2+2H2O
So the molar ratio between ca(oh)2 and hcl is 1 is to 2
Thus with each mole of ca(oh)2 the 2 moles of hcl will react
As a result for a complete reaction we need 7 mole of HCL 
Molarity of hcl is 0.85 
so number of litres of hcl needed would be 8.2 as
number of moles of hcl=8.2x0.85=7moles
So 
ANSWER IS B 8.2 L OF HCL