1.6 x 10⁻¹⁰ M is the concentration of OH− ion of the solution has a pH of 4.20.
pH of any solution is define as the negative logarithm of the concentration of hydrogen ions i.e. pH = -log[H⁺].
Equation of pH will be written in the form of base 10 by removing the log as:
[H⁺] = [tex]10^{-pH}[/tex]
Given value of pH is 4.20 and concentration of H⁺ ions will be calculated as:
[H⁺] = 10⁻⁴°²⁰
[H⁺] = 6.3 × 10⁻⁵
Now the relation between pH & pOH in term of base 10 is:
[H⁺][OH⁻] = 10⁻¹⁴
[OH⁻] = 10⁻¹⁴ / [H⁺]
[OH⁻] = 10⁻¹⁴ / 6.3 × 10⁻⁵ = 1.6 x 10⁻¹⁰ M
Hence, option (E) is correct i.e. 1.6 x 10⁻¹⁰ M.
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