A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish orange. Which of the following would change the colour of this pH paper to greenish blue?

Question

$\begin{array}{1 1} \text{(a) lemon juice } \\ \text{(b) Vinegar} \\ \text{ (c)Common salt} \\ \text{(d) An antacid} \end{array}$