Question

1. isotopes are atoms of the same element that have different

a. principal chemical properties.
b. numbers of protons.
c. masses.
d. numbers of electrons.

Explanation:

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<reasoning>

Define isotopes

\[
\text{Isotopes} = \text{atoms of the same element with the same number of protons but different numbers of neutrons}
\]

Relate to atomic mass

\[
\text{Atomic Mass} = \text{protons} + \text{neutrons}
\]
\[
\text{Different number of neutrons} \implies \text{different atomic masses}
\]

Evaluate options

\[

$$\begin{aligned} &\text{a. principal chemical properties} \implies \text{Incorrect (determined by electrons/protons, which are identical)} \\ &\text{b. numbers of protons} \implies \text{Incorrect (same element must have the same number of protons)} \\ &\text{c. masses} \implies \text{Correct (different number of neutrons results in different masses)} \\ &\text{d. numbers of electrons} \implies \text{Incorrect (neutral atoms of the same element have the same number of electrons)} \end{aligned}$$

\]
</reasoning>

<answer>
<mcq-option>a. principal chemical properties.</mcq-option>
<mcq-option>b. numbers of protons.</mcq-option>
<mcq-correct>c. masses.</mcq-correct>
<mcq-option>d. numbers of electrons.</mcq-option>
</answer>

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Answer:

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<reasoning>

Define isotopes

\[
\text{Isotopes} = \text{atoms of the same element with the same number of protons but different numbers of neutrons}
\]

Relate to atomic mass

\[
\text{Atomic Mass} = \text{protons} + \text{neutrons}
\]
\[
\text{Different number of neutrons} \implies \text{different atomic masses}
\]

Evaluate options

\[

$$\begin{aligned} &\text{a. principal chemical properties} \implies \text{Incorrect (determined by electrons/protons, which are identical)} \\ &\text{b. numbers of protons} \implies \text{Incorrect (same element must have the same number of protons)} \\ &\text{c. masses} \implies \text{Correct (different number of neutrons results in different masses)} \\ &\text{d. numbers of electrons} \implies \text{Incorrect (neutral atoms of the same element have the same number of electrons)} \end{aligned}$$

\]
</reasoning>

<answer>
<mcq-option>a. principal chemical properties.</mcq-option>
<mcq-option>b. numbers of protons.</mcq-option>
<mcq-correct>c. masses.</mcq-correct>
<mcq-option>d. numbers of electrons.</mcq-option>
</answer>

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