The pH values of two acids A and B are $1$ and $5$ respectively. Which is the strong acid?

The pH scale

• The pH scale is a simple way to represent the acidity and alkalinity of aqueous solutions.
• The hydrogen ion $\left({\mathrm{H}}^{+}\left(\mathrm{aq}\right)\right)$ index is referred to as pH. As a result, acid strength is determined by the concentration of hydrogen ions.
• The pH is also calculated using the negative logarithm (to the base $10$) of the hydrogen ion concentration given in moles per liter.

$\mathrm{pH}=-{\log }_{10}\left[{\mathrm{H}}^{+}\left(\mathrm{aq}\right)\right]$

pH value

• The condition of pure water in alkalinity, i.e., the condition of exact neutrality, is represented by the number $7$ on the pH scale.
• The number of hydrogen ion $\left({\mathrm{H}}^{+}\left(\mathrm{aq}\right)\right)$and hydroxide ion $\left({\mathrm{OH}}^{-}\left(\mathrm{aq}\right)\right)$ in pure water is equal.

${\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{H}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)\left[\mathrm{at}25°\mathrm{C}\right]$

• pH levels below $7$ indicate acidity, whereas pH values over $7$ indicate basicity.

The pH values of two acids, A and B, are $\mathbf{1}$ and $\mathbf{5}$:

• Acid A has a low pH value that is $1$. In comparison to B, which has a pH of $5$, A is a strong acid.