Answer
No, (a) is not the most basic solution.
Work Step by Step
- $2.0 \times 10^{-5}$ mol $HBr$; in $1.00L$ = $2.0\times 10^{-5}M$
- $HBr$ is a strong acid, therefore: $[H_3O^+] = [HBr] = 2.0 \times 10^{-5}M$
- Now, use this value to calculate the hydroxide concentration.
$[H_3O^+] * [OH^-] = Kw = 10^{-14}$
$ 2 \times 10^{- 5} * [OH^-] = 10^{-14}$
$[OH^-] = \frac{10^{-14}}{ 2 \times 10^{- 5}}$
$[OH^-] = 5 \times 10^{- 10}M$
The most basic solution is the one with the greatest hydroxide concentration.
Since (b) : $[OH^-] = 5 \times 10^{-9}M$, (b) has the greater hydroxide concentration, so, it is the most basic solution.
