Which of these has the lowest pH value?

Hydrochloric acid is the correct choice because it is a strong acid with a very low pH value, typically around 1 to 2 in concentrated form. The pH scale ranges from 0 to 14, with values below 7 indicating acidity. The lower the pH, the stronger the acidity.

In comparison, water has a neutral pH of 7, vinegar generally has a pH around 2.5 to 3, and lemon juice is slightly more acidic, usually around 2 to 3. Therefore, while vinegar and lemon juice are both acidic, they do not reach the extreme acidity of hydrochloric acid, which is significantly lower on the pH scale. This makes hydrochloric acid the option with the lowest pH value among the choices given.