Option 1 states that boric acid is an acid because its molecule accepts OH from water, releasing a proton. This means that when boric acid is dissolved in water, it reacts with water molecules to form an equilibrium between the acid and its conjugate base. The boric acid molecule accepts a hydroxide ion (OH-) from water and releases a proton (H+), leaving behind the conjugate base of boric acid.

Option 2 suggests that boric acid combines with a proton from a water molecule. However, this is not a correct explanation as it does not accurately describe the behavior of boric acid.

Option 3 states that boric acid contains a replaceable H+ ion. This is a possible explanation for why boric acid is an acid. However, it does not fully explain the reaction of boric acid with water.

Option 4 suggests that boric acid gives up a proton. This is similar to option 1 and provides a more concise explanation. However, option 1 is still a better choice as it explicitly mentions the acceptance of OH from water.

In conclusion, option 1 provides the most accurate explanation for why boric acid is an acid.