Question

which solution below has the lowest concentration of hydroxide ions?
○ ph=7.93
○ ph=10.12
○ ph=7.00
○ ph=3.21
question 23 (0.0862 points)
isotopes are
○ atoms of the same element that have different number of electrons.
○ atoms of the same element that have different number of neutrons.
○ atoms of the same element that have different number of protons.
○ none of these

Explanation:

First Question (Hydroxide Ion Concentration)

Step1: Recall pH and pOH relation

We know that \( \text{pH} + \text{pOH} = 14 \), and \( \text{pOH} = -\log[\text{OH}^-] \), so \( [\text{OH}^-] = 10^{-\text{pOH}} = 10^{- (14 - \text{pH})} \). Lower \( [\text{OH}^-] \) means more acidic (lower pH, since pH and \( [\text{OH}^-] \) are inversely related for aqueous solutions at 25°C).

Step2: Compare pH values

The pH values are 7.93, 10.12, 7.00, 3.21. The lowest pH (most acidic) is 3.21, which means the lowest \( [\text{OH}^-] \) (since acidic solutions have less \( \text{OH}^- \) than basic or neutral).

Isotopes are defined as atoms of the same element with the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers). The first option is wrong (different electrons relate to ions), third is wrong (same element has same protons), so the second option is correct.

Answer:

\( \text{pH}=3.21 \)

Second Question (Isotopes)