Chemistry · d- and f-block elements · chapter 4 of 10

Class 12 Chemistry Chapter 4: The d- and f-Block Elements Assertion-reason questions with answers

2 assertion-reason questions on The d- and f-Block Elements, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, 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): Aqueous solutions of Ti⁴⁺ salts are colourless. Reason (R): Ti⁴⁺ has the configuration 3d⁰, so no d–d transition is possible.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Colour arises from an electron being excited between d orbitals. Ti⁴⁺ (Z = 22, [Ar]3d⁰) has no d electron to excite, which is exactly why it is colourless.

Question 2
Assertion (A): Potassium dichromate is used as a primary standard in volumetric analysis. Reason (R): The chromate ion is tetrahedral.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both statements are true, but the shape of the chromate ion has nothing to do with K₂Cr₂O₇'s use as a primary standard, which rests on its being a strong oxidant obtained as a pure, weighable crystalline salt.

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