how many ml of .5M HCL are required to neutralize 600 mg of Mg(OH)2?
convert 600mg to moles.
2HCl + Mg(OH)2 = MgCl2 + 2H2O
so, each mole of Mg(OH)2 needs 2 moles of HCl. So, now you know how many moles of HCl you need.
For .5M HCl solution, you will need 2L (2000ml) of acid for each mole.