Question:

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R)
Assertion (A): The first ionization enthalpy of $3d$ series elements is more than that of group 2 metals
Reason (R): In $3d$ series of elements successive filling of d-orbitals takes place
In the light of the above statements, choose the correct answer from the options given below :

Updated On: Sep 30, 2024
  • Both $( A )$ and $( R )$ are true and $( R )$ is the correct explanation of $( A )$
  • (A) is true but (R) is false
  • (A) is false but (R) is true
  • Both $( A )$ and $( R )$ are true but $( R )$ is not the correct explanation of $( A )$
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The Correct Option is C

Solution and Explanation

From Sc to Mn ionization energy is less than that of Mg. 
For 3d series :
 ScTiVCrMn
IE (KJ/mol)631656650653717
 FeCoNiCuZn
IE (KJ/mol)762758736745906

For 2nd Group

 BeMgCaSrBaRa
IE (KJ/mol)631656650653717762
So , the correct option is (C) : (A) is false but (R) is true
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Concepts Used:

Classification of Elements & Periodicity in Properties

Since many elements were being discovered in the 19th century and the study of these elements individually was proving difficult, classification of elements was made necessary.

Classification by Johann Dobereiner - German chemist Johann Dobereiner classified certain elements on the basis of their similar properties in the groups of continuing - three elements each. These groups were called ‘triads’. In every triad, the atomic weight of the middle element was equal to the average of the atomic weights of the first and third elements. 

Newlands Law of Octaves - The elements were arranged in increasing order of their atomic weights and found that every 8th element shows similarity with the 1st element. 

Mendeleev’s Periodic Table - The arrangement of all 63 elements in rows or columns in order of their atomic weight was made by Mendeleev. He left some space for corresponding elements in his periodic table which were not even discovered till then. Although he predicted the properties of those elements through his periodic classification of elements. 

Modern Periodic Law - The properties of the elements of the modern periodic law are periodic functions of their atomic numbers.