Answer:
0.0634 M HCl
Explanation:
Since HCl and NaOH react in a one-to-one mole ratio, we can just use M1V1 = M2V2 to solve for M1 (the concentration of HCl)
M1 = ? M HCl
V1 = 24.30 mL HCl
M2 = 0.120 M NaOH
V2 = 12.84 mL NaOH
M1(24.30 mL HCl) = (0.120 M NaOH)(12.84 mL NaOH)
M1 = 0.0634 M HCl