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Chemistry

Classification of Elements and Periodicity in Properties

A Chemistry chapter of the NEET syllabus, and how to practise it for the computer-based exam.

Exam rules change between cycles. Confirm dates, syllabus and pattern against NTA's official site. We are not NTA.

Weightage: what the paper actually did

Classification of Elements and Periodicity in Properties carried 4 questions in the NEET 2026 paper. One paper is a data point, not a destiny: NTA moves weight between chapters every cycle, which is why the weightage tables deserve care. The stable facts are the paper's shape: 180 questions, 720 marks, +4 right, −1 wrong.

Sample PYQs from this chapter

Real questions NTA asked from Classification of Elements and Periodicity in Properties, with the answer and the working. Try before you peek.

Question 1 · NEET 2026

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 O is lower than that of N and F. Reason (R): The loss of an electron from O leads to stable half-filled p orbital In light of the above statements, choose the most appropriate answer from the options given below:
  1. A.Both A and R are correct and R is the correct explanation of A
  2. B.Both A and R are correct and R is NOT the correct explanation of A
  3. C.A is correct but R is not correct.
  4. D.A is not correct but R is correct
Answer and explanation

Answer: A

Oxygen is [He]2s22p4[\mathrm{He}]2\mathrm{s}^2 2\mathrm{p}^4; the fourth 2p electron must pair up in an already-occupied orbital and suffers extra repulsion, so it is comparatively easy to remove. Losing it gives O+\mathrm{O}^{+} with the 2p32\mathrm{p}^3 half-filled configuration, which is extra stable through exchange energy. That is precisely why oxygen's first ionization enthalpy dips below nitrogen's despite nitrogen having a smaller nuclear charge, and stays below fluorine's. R therefore explains A. NCERT Class 11, Classification of Elements and Periodicity in Properties.

Question 2 · NEET 2026

Identify the incorrect statement from the following:
  1. A.The largest and the smallest species among Mg, Mg2+\mathrm{Mg}^{2+}, Al and Al3+\mathrm{Al}^{3+} are Al and Mg2+\mathrm{Mg}^{2+} respectively.
  2. B.The IUPAC name of the element with atomic number 107 is Unnilseptium.
  3. C.The similarity in behaviour of Li with Mg is referred to as 'diagonal relationship'.
  4. D.The oxidation state and covalency of Al in [AlCl(H2O)5]2+[\mathrm{AlCl}(\mathrm{H}_{2}\mathrm{O})_{5}]^{2+} are 3 and 6, respectively.
Answer and explanation

Answer: A

Cationic size decreases with increasing positive charge and across a period, so among Mg, Mg2+\mathrm{Mg}^{2+}, Al and Al3+\mathrm{Al}^{3+} the largest species is neutral Mg and the smallest is Al3+\mathrm{Al}^{3+}, not Al and Mg2+\mathrm{Mg}^{2+}; hence statement A is incorrect and is the answer. The others are correct: element 107 is Unnilseptium, Li and Mg show a diagonal relationship, and Al in the given complex has oxidation state +3 with covalency 6.

How to practise Classification of Elements and Periodicity in Properties

Chapter by chapter, against real past-paper questions, on a screen: NEET is computer based from 2027. Read the chapter once, then attempt its PYQs until your accuracy stops climbing, and let the wrong answers tell you which lines to reread. If the chapter keeps refusing to stick, that has its own guide. There is also a free NEET mini mock with answers.

Nearby Chemistry chapters

Questions

How many questions did Classification of Elements and Periodicity in Properties have in NEET 2026?

Classification of Elements and Periodicity in Properties carried 4 questions in the NEET 2026 paper. Weightage shifts between cycles, so treat it as a probability, not a promise.

Where can I practise Classification of Elements and Periodicity in Properties PYQs for NEET?

Explore available chapter-wise NEET practice in BrainIt, free until the 2027 exam. Review explanations and track chapter accuracy to guide your revision. Sample questions from this chapter are on this page.

Is Classification of Elements and Periodicity in Properties important for NEET 2027?

It is part of the Chemistry syllabus the paper draws from, and NEET 2027 is computer based, so practise it on a screen. Your own accuracy in the chapter matters more than any weightage table: a heavy chapter you already score well on needs less time than a light one you keep missing.

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