Chemistry
Assertion (A): Cobalt (atomic mass 58.94) is placed before Nickel (atomic mass 58.68) in Mendeleev's periodic table.
Reason (R): Physical and chemical properties of the elements are a periodic function of their atomic masses.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Periodic Table
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Answer
Both A and R are true but R is not the correct explanation of A.
Explanation — Cobalt with atomic mass 58.94 is placed before Nickel with atomic mass 58.68 in Mendeleev's periodic table. They are anomalous pair which do not follow mendeleev's principle. Hence the assertion is true.
Mendeleev's periodic law states that physical and chemical properties of the elements are a periodic function of their atomic masses. Hence the reason (R) is true.
However, reason (R) does explain why cobalt is placed before nickel in mendeleev's periodic table. Hence reason (R) is not the correct explanation of assertion (A).
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