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Classification of Elements and Periodicity

15 NEET questions on Classification of Elements and Periodicity. A sample is shown below with full explanations; the rest are available free after signing up.

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Classification of Elements and Periodicity2026medium

Q1.Among the following options, the correct trend in the electron gain enthalpy is

  • AF > Cl > Br > I
  • BBr > Cl > F > I
  • CCl > F > Br > IAnswer
  • DI > Br > Cl > F

Explanation

Chlorine, not fluorine, releases the most energy on gaining an electron. Fluorine's 2p subshell is so compact that the incoming electron meets strong repulsion from those already there, which offsets its high nuclear attraction. So the order of magnitude runs Cl > F > Br > I rather than straight down the group.

Source: NEET 2026 re-exam (21 June), Code 50, Q53

Classification of Elements and Periodicity2026medium

Q2.Given below are two statements: In light of the above statements, choose the most appropriate answer from the options given below:

  • 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 a stable half-filled p orbital.
  • ABoth A and R are correct and R is the correct explanation of AAnswer
  • BBoth A and R are correct and R is NOT the correct explanation of A
  • CA is correct but R is not correct
  • DA is not correct but R is correct

Explanation

Oxygen is 2p⁴, so one of its p orbitals holds a pair and suffers extra electron-electron repulsion. Removing that electron leaves the stable half-filled 2p³ arrangement, which is exactly why oxygen ionises more easily than nitrogen despite the smaller nuclear charge — the reason genuinely explains the assertion.

Source: NEET 2026 re-exam (21 June), Code 50, Q70

Classification of Elements and Periodicity2025hard

Q3.Which of the following statements are true?

  • A. Unlike Ga that has a very high melting point, Cs has a very low melting point.
  • B. On Pauling scale, the electronegativity values of N and Cl are not the same.
  • C. Ar, K⁺, Cl⁻, Ca²⁺ and S²⁻ are all isoelectronic species.
  • D. The correct order of the first ionization enthalpies of Na, Mg, Al and Si is Si > Al > Mg > Na.
  • E. The atomic radius of Cs is greater than that of Li and Rb.
  • AA, B and E only
  • BC and E onlyAnswer
  • CC and D only
  • DA, C and E only

Explanation

A is false because Ga has an unusually LOW melting point (302.9 K — it melts in the hand), so the premise of the contrast is wrong. B is false: on the Pauling scale N and Cl are both 3.0. C is true — every species listed has 18 electrons. D is false because Al has a lower first ionisation enthalpy than Mg (removing a 3p electron is easier than breaking the filled 3s²), so the order is Si > Mg > Al > Na. E is true, since atomic radius increases down group 1.

Source: NEET 2025 (4 May), Code 45, Q47

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Questions are reformatted from NEET previous year papers with original explanations and topic tagging. NEET Prep is not affiliated with the NEET examining body.