How did Dmitri Mendeleev arrange the elements in his original periodic table?

• A. By increasing atomic number
• B. By chemical reactivity
• C. By increasing atomic mass
• D. By alphabetical order

Answer: (C)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the first widely recognized periodic table in the 19th century before the discovery of the atomic number.
2. Recall that Mendeleev arranged elements based on a property that was known at the time and could be measured for all elements: atomic mass.
3. Recognize that Mendeleev noticed patterns in the properties of elements when they were ordered by increasing atomic mass, which allowed him to predict the existence and properties of undiscovered elements.
4. Note that the concept of atomic number (number of protons) was not known during Mendeleev's time, so he could not have arranged elements by atomic number.
5. Conclude that Mendeleev's original periodic table was arranged by increasing atomic mass, which is why the correct answer is 'By increasing atomic mass.'