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Fill in the following blanks with suitable words:
(a) Acids have a pH...........than 7.
(b) Alkalis have a pH.............. than 7.
(c) Neutral substances have a pH of ................
(d) The more acidic a solution, the ................. the pH.
(e) The more alkaline a solution, the............... the pH.

Answer
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Hint: To answer this question, you should recall the concept of pH scale and the properties of acid and base. It ranges from 1 to 14 and is the negative logarithm of the hydrogen ion concentration.

Complete step by step answer:
The pH scale is a logarithmic scale that is used to measure the acidity or the basicity of a substance. The possible values on the pH scale range from 0 to 14. The term pH is an abbreviation of potential for hydrogen.
 Acidic substances have pH values ranging from 1 to 7 and alkaline or basic substances have pH values ranging from 7 to 14. A perfectly neutral substance would have a pH of exactly 7.
The pH of a substance can be expressed as the negative logarithm of the hydrogen ion concentration in that substance. Similarly, the pOH of a substance is the negative logarithm of the hydroxide ion concentration in the substance. These quantities can be expressed via the following formulae:pH = log[H + ] and pOH = log[OH-]. Hence the statements can be filled as:
(a) Acids have a pH lower than 7.
 (b) Alkalis have a pH greater than 7
 (c) Neutral substances have a pH of 7.
 (d) The more acidic a solution, the lower the pH.
 (e) The more alkaline a solution, the higher the pH.

Note:
You should know about the limitations of pH Scale
pH values do not reflect directly the relative strength of acid or bases: A solution of pH = 1 has a hydrogen ion concentration 100 times that of a solution of pH = 3 (not three times).
pH value is zero for 1N the solution of the strong acid. The concentration of 2N, 3N, 10N,etc. gives negative pH values.
A solution of an acid having very low concentration, say 108N, shows a pH = 8and hence should be basic, but actual pH value is less than 7.