Question

Assertion: According to Mendeleev, the properties of elements are a periodic function of their atomic weights.
Reasons: Mendeleev left the gap under aluminium and a gap under silicon, and called these elements Eka-Aluminium and Eka-Silicon.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect
D) Both Assertion and Reason are incorrect.

Answer 1

Hint: Try to recall that Mendeleev arranged 63 elements and carefully examined the relationship between atomic weights of elements and their physical and chemical properties. Now, by using this you can easily answer the question.

Complete step by step solution:
It is known to you that Mendeleev in 1963 proposed his periodic law.

According to Mendeleev periodic law, the physical and chemical properties of elements are a periodic function of their atomic weights, i.e., when the elements are arranged in order of their increasing atomic weights, elements with similar properties are repeated after regular intervals.
This repetition of properties of elements after certain regular intervals is called periodicity of properties.
Mendeleev arranged the then-known elements in order of their increasing atomic weights, grouping together elements with similar properties and leaving out blank ones.
Mendeleev also left gaps under aluminium and a gap under silicon and called these elements Eka-aluminium and Eka-silicon because he believed that these would be similar to aluminium and silicon respectively.
These elements were discovered later and Mendeleev’s predictions were found to be remarkably correct.
Therefore, from above we can conclude that both assertion and reason are correct but the reason is not the correct explanation of assertion.

So option B is the correct option.

Note:

It should be remembered to you that in Mendeleev’s periodic table, some elements with higher atomic weights precede the elements with lower atomic weight.
Also, you should remember that in Mendeleev’s periodic table, isotopes were placed separately and no proper place has been alloted to noble gases.