Answer: M₂ = 0
Explanation:
HCl + NaOH — NaCl + H2O
For acid base titrations:
M₁ V₁ = M₂ V₂
where lower-script 1 and 2 are the molarity and volume for acid and base respectively.
M₁ = 0.30 M
V₁ = 12.5 ml
M₂ = (unknown)
V₂ = 285
0.30 x 12.5 = 285 M₂
M₂ = 3.8/ 285
M₂ = 0
p.s I think there is an error with the typed question. It’s not possible to use 285 ml of base against 12.5 ml of acid.