How many hydroxide ions are needed to completely neutralize 1.0 liter of 0.50 m hcl?

The  number of hydroxide ions that are needed to completely neutralize 1.0 liter  of  0.50M HCl  is  calculated as below

find the  moles of H^+ used  from HCl
moles = molarity  x  volume
  = 0.50 x 1  =0.50  moles of  H^+  used

write ionic equation  for reaction

that is H ^+  + OH^-  = H2O

by  use of  mole  ratio between H^+ to OH^-  which  is 1:1 the moles of OH^- used = 0.50 x1/1 = 0.50  moles

By  use of Avogadro  law  constant

1  mole =  6.02 x10^23 ions
what about 0.5  moles

= 0.5 moles/ 1 moles  x 6.02  x10^23  = 3.01 x10^23 ions of OH^-