NaOH+ HCl -> NaCl+ H2O
Based on the above balanced equation, we know that 1 mol HCl= 1 mol NaOH (keep it in mind; it will be used later)
We know that 0.20M HCl solution (soln)= 0.20mol HCl/1L HCl soln (this one is based on the definition of molarity).
First, we have to find the mole of HCl:
5.0mL HCl solution (1L soln/ 1,000mL soln) (0.20mol HCl/1L HCl soln)= 1.010^(-3)mol HCl.
Now that we know the mole of HCl, let's find the molarity of NaOH:
1.010^(-3)mol HCl (1mol NaOH/1 mol HCl) (1/10.mL NaOH soln)* (1,000mL NaOH soln/1L NaOH soln)= 0.10mol/L NaOH soln = 0.10M NaOH soln
Hope this would help :))
