Question

A lower pH means:
A. Higher basicity
B. Lower acidity
C. Higher acidity
D. Both A and C

Answer 1

Hint: pH can be measured on the pH scale from 0(highly acidic) to 14(highly basic). Higher the hydrogen ion concentration of a substance, lower is the pH value.
For a neutral solution, pH value is 7. If the pH value is less than 7, it represents an acidic solution and if it is higher than 7, it represents a basic solution.

Complete step by step answer:
A universal indicator is a mixture or a combination of several indicators which is added to a substance to determine its pH. pH can be considered as a number that indicates the acidic or basic nature of a solution.
pH is measured by universal indicator which changes colour in different pH environments. It appears red at low pH, violet/blue at high pH and green at neutral pH.
pH of a solution is actually the negative logarithm of the hydronium ion concentration in moles per litre.
$\text{pH = - log}\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{ + }}\right]$
We know that all acidic solutions have hydronium ion concentration greater than $1.0\times {10}^{-7}$ . This means, the hydronium ion concentration in an acidic solution may be ${10}^{-6}$ , ${10}^{-5}$ , ${10}^{-4}$ etc.
If an acidic solution has hydronium ion concentration ${10}^{-6}$ , then pH of the acidic solution will be:
 $$\begin{gathered} \text{pH = - log}\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{ + }}\right] \\ \Rightarrow \text{pH = - log}\left[{10}^{-6}\right] \\ \Rightarrow \text{pH = }6 \end{gathered}$$
Thus, pH values of all acidic solutions will be less than 7. So, a lower pH will indicate higher acidity.

So, the correct option is C.

Note:
pH has a great importance in biochemical reactions such as digestion of food. Human blood has a pH of $7.4$ . If it changes by $0.2$ pH units, then death results.
pH also has a great importance in agriculture. Soil is tested to determine whether acidic or basic fertilizer is required for a particular crop to be grown in that soil.