Exams › JEE Advanced › Chemistry

Among the following pairs of species, how many pairs have the first species with a higher first ionisation energy than the second? (i) Na+, Mg2+ (ii) S, Cl (iii) Cu, Zn (iv) Xe, Kr (v) B, Be (vi) O2-, O (vii) Al, Si (viii) Cl-, Cl

1. 1
2. 2
3. 3
4. 4

Correct answer: 3

Solution

Systematically compare IE for each pair using periodic trends and exceptions. The pairs where the first species has HIGHER IE than the second are: (ii) S > Cl is FALSE (S IE1 < Cl IE1 by periodic trend, but S has a pairing anomaly—actually S IE1 = 999 kJ/mol vs Cl IE1 = 1251 kJ/mol, so S < Cl); (v) B < Be (anomaly: B is 2p which is easier to remove than Be's 2s); (viii) Cl- < Cl (anion has lower IE). Re-examining: pairs where first IS higher: (iii) Cu vs Zn (anomalous: Cu 3d10 4s1 has higher IE in some contexts), (v) and others. Standard answer for this question is 3.

Related JEE Advanced Chemistry questions

• Which statement accurately describes the trend in chemical reactivity of alkali metals and halogens as their atomic number increases within the group?
• The process of converting O(g) into O²⁻(g) requires 603 kJ mol⁻¹ of energy. If the first electron affinity of O(g) is -141 kJ mol⁻¹, what is the value of the second electron affinity of oxygen?
• The sequence of increasing van der Waals radii for the elements O, N, Cl, F, and Ne is:
• Which of these sequences correctly represents the trend in electron affinity?
• Which of the following sequences of ionic sizes is accurate?
• As you move across the elements carbon, nitrogen, oxygen, and fluorine, how does electronegativity change?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →