(a) What does the pH of a solution signify? Three solutions A,B and C have pH values of $6,4$ and $10$ respectively. Which of the solutions is highly acidic?
(b) A farmer has found that the pH of soil in his fields is $4.2$ . Name any two chemical materials which he can mix with the soil to adjust its pH.

Hint: Find out for what pH values the solutions are acidic and basic and also the neutral point. If the pH value is lesser than the neutral point then the solution would be acidic and if the pH value is more than the neutral value then the solution will be basic.

Complete answer:
(a) The letters pH stand for potential of hydrogen and it is a measure of the concentration of hydrogen ions in a solution. The pH of a solution signifies the acidity or basicity of the solution.
A solution is said to be neutral if the pH value is $7$ , if the pH value is less than $7$ then it is acidic in nature and if the pH value is more than $7$ then the solution is basic in nature.
Here, the pH value of A is given as $6$ which is less than the neutral value so it is an acidic solution.
The pH value of B is given to us as $4$ so it is an acidic solution.
The pH value of C is $10$ and hence it is a basic solution.

(b) The pH of the soil is given as $5.2$ which is acidic in nature. So in order to neutralize this acidity we need to mix basic chemical materials. Some of the examples could be chalk, calcium hydroxide, calcium oxide etc.

Note:
The neutral pH value is $7$ . Any solution with pH value less than seven is acidic in nature and any solution with pH value more than seven is basic in nature. Solutions with values closer to $7$ are either weakly acidic or weakly basic.