Chemistry · Classification of elements and periodicity · chapter 3 of 9

Class 11 Chemistry Chapter 3: Classification of Elements and Periodicity in Properties Assertion-reason questions with answers

2 assertion-reason questions on Classification of Elements and Periodicity in Properties, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): The metallic character of the alkali metals increases from lithium to caesium. Reason (R): Down the group the outermost electron is farther from the nucleus and more shielded, so less energy is needed to remove it.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. Metallic character is the tendency to lose electrons; the falling ionization enthalpy down the group, caused by larger size and greater shielding, is exactly why it rises.

Question 2
Assertion (A): Zinc, cadmium and mercury do not show most of the properties typical of transition elements. Reason (R): All the d-block elements are metals.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true, but R does not explain A. Zn, Cd and Hg differ because their configuration is (n − 1)d¹⁰ns², with a completely filled d subshell, not because they are metals.

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