Question

Assertion: According to Mendeleev, periodic properties of elements are periodic functions of their atomic number.
Reason: Atomic number is equal to the number of protons.
A. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are correct, but Reason is not the correct explanation of assertion.
C. Assertion is correct but Reason is incorrect.
D. Assertion is incorrect but Reason is correct.

Answer 1

Hint:Determine the basis of classification of elements in Mendeleev periodic table and modern periodic table. Also determine the difference between the atomic number and the mass number.

Complete answer:
According to Mendeleev, periodic properties of elements are periodic functions of their atomic weight.
According to Moseley's periodic law, periodic properties of elements are periodic functions of their atomic number.
Hence, the Assertion is incorrect.
Atomic number is equal to the number of protons. It is also equal to the number of electrons. The mass number is equal to the sum of the number of protons and the number of neutrons.
Hence, the Reason is correct.

Hence, the correct option is the option D. Assertion is incorrect but Reason is correct.

Additional information:
 In the Mendeleev periodic table, the elements are arranged in the increasing order of their atomic weights. In modern periodic tables, the elements are arranged in the increasing order of their atomic numbers.

Note:
You can obtain the number of electrons in a neutral atom from its atomic number. You can also obtain the number of protons from the atomic number. To obtain the number of neutrons, you subtract the atomic number from the mass number.