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On the periodic table, elements in the same row are arranged from left to right by

Rationale

An increasing number of protons in an atom's nucleus.

Elements in the same row of the periodic table, known as periods, are organized from left to right based on their atomic number, which corresponds to the number of protons in their nuclei. This arrangement reflects the sequential addition of protons as one moves across the table, leading to a systematic increase in atomic number and corresponding properties.

A (an increasing number of neutrons in an atom's nucleus) YOUR ANSWER

While the number of neutrons can vary among isotopes of the same element, the arrangement of elements in a row on the periodic table is not based on neutron count. Instead, neutron numbers can vary independently of the element's position on the periodic table, meaning this choice does not accurately represent how elements are organized.

B (a decreasing number of neutrons in an atom's nucleus) YOUR ANSWER

Similar to choice A, this option fails to describe the organization of elements in the periodic table. Neutron numbers may decrease or increase without following the left-to-right arrangement of elements, which is determined solely by proton count. Thus, this choice does not reflect the underlying principle of the periodic table's structure.

C (an increasing number of protons in an atom's nucleus) CORRECT

This is the correct answer as it directly addresses the systematic increase in atomic number across a period. Each element in a row has one more proton than the element to its left, which is the fundamental basis for the organization of the periodic table and the resulting chemical properties of each element.

D (a decreasing number of protons in an atom's nucleus) YOUR ANSWER

This statement contradicts the fundamental organization of the periodic table. As one moves from left to right, the number of protons increases, not decreases. Therefore, this choice misrepresents the arrangement criteria and does not apply.

Conclusion

The periodic table is structured such that elements in the same row are arranged by an increasing number of protons in their nuclei, reflecting their atomic number. Each subsequent element represents a new proton added to the nucleus, which defines its identity and influences its chemical properties. Neutron counts and variations do not determine this organization, making the proton count the key characteristic for the arrangement of elements in the periodic table.

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