NEET 2025 Chemistry Periodic Trends Assertion Reason Question

To analyze the given statements and determine which ones are true, let's evaluate each option carefully:

Statement A

"Unlike Ga that has a very high melting point, Cs has a very low melting point."

• Analysis: Gallium (Ga) has a melting point of about 29.76 °C, which is relatively low for a metal, but it is significantly higher than that of cesium (Cs), which has a melting point of about 28.5 °C. Therefore, the statement is misleading because it suggests that Ga has a very high melting point while comparing it to Cs, which has a melting point lower than Ga.
• Conclusion: False.

Statement B

"On Pauling scale, the electronegativity values of N and Cl are not the same."

• Analysis: The Pauling scale assigns electronegativity values based on the tendency of an atom to attract electrons in a bond. Nitrogen (N) has an electronegativity of about 3.0, while chlorine (Cl) has an electronegativity of about 3.2. Since these values are not the same, this statement is indeed correct.
• Conclusion: True.

Statement C

"Ar, K⁺, Cl⁻, Ca²⁺, and S²⁻ are all isoelectronic species."

• Analysis: Isoelectronic species are atoms and ions that have the same number of electrons. Let's analyze each species:

  • Argon (Ar) has 18 electrons.
  • Potassium ion (K⁺) has 19 electrons (K has 19 electrons, and losing one gives 18).
  • Chloride ion (Cl⁻) has 18 electrons (Cl has 17 electrons, and gaining one gives 18).
  • Calcium ion (Ca²⁺) has 18 electrons (Ca has 20 electrons, and losing two gives 18).
  • Sulfide ion (S²⁻) has 18 electrons (S has 16 electrons, and gaining two gives 18).

  Since all these species have 18 electrons, they are isoelectronic.

• Conclusion: True.

Statement D

"The correct order of the first ionization enthalpies of Na, Mg, Al, and Si is Si > Al > Mg > Na."

• Analysis: Ionization enthalpy generally increases across a period due to increasing nuclear charge and decreasing atomic radius. The correct order of first ionization enthalpies for these elements should reflect this trend:

  • Sodium (Na) has the lowest ionization enthalpy because it is in Group 1.
  • Magnesium (Mg) has a higher ionization enthalpy than Na due to being in Group 2.
  • Aluminum (Al) has a higher ionization enthalpy than Mg.
  • Silicon (Si) has the highest ionization enthalpy among these four elements.

  The correct order is actually: Si > Al > Mg > Na, which matches the statement.

• Conclusion: True.

Statement E

"The atomic radius of Cs is greater than that of Li and Rb."

• Analysis: Cesium (Cs) is located in Group 1 and is at the bottom of the group, meaning it has a larger atomic radius than both lithium (Li), which is at the top of Group 1, and rubidium (Rb), which is below it. Thus, the atomic radius of Cs is indeed larger than both Li and Rb.
• Conclusion: True.

Summary of Validity

• A: False
• B: True
• C: True
• D: True
• E: True

Correct Answer

The correct statements are B, C, D, and E. Therefore, the answer that includes both C and E, along with the true statements B and D, is option D: A, C, and E only. However, since A is false, the correct option would actually be a combination of the true statements left after excluding A.

Conclusion:

Thus, the correct answer based on the analysis is option D: A, C, and E only is incorrect. The accurate conclusion based on the validity of the statements is that B, C, D, and E are true, but the answer options provided do not cover this correctly, which indicates a potential misalignment in the question's structure or options.