The equation used to represents the electron gain enthalpy is

• X(g) + e^- → X^-(g)

• X(s) + e^- → X^-(g)

• X(g) → X⁺(g) + e^-

• X(s) → X⁺(g) + e^-

An element in +2 oxidation state has 24 electrons. The atomic number of the element and the number of unpaired electrons in it respectively are

• 24 and 4

• 26 and 4

• 24 and 2

• 26 and 5

Among the following, the isoelectronic specie (s) is/are

(i)  O^2-, F^-, Na⁺, Mg²⁺

(ii) Na⁺, Mg⁺, Al³⁺, F^-

(iii) N^3-,  O^2-, F^-, Ne

• (i) and (ii)

• (i), (ii) and (iii)

• (ii) and (iii)

• (i) and (iii)

What is the atomic number of the element with symbol Uus?

• 117

• 116

• 115

• 114

The increasing order of the first ionisation enthalpies of the elements B, P, S and F is 

• B < S < P < F

• F < S < P < B

• P < S < B < F

• B < P < S < F

The electronic configuration of ₅₉Pr ( praseodimium) is

• [₅₄Xe] 4f²5d¹6s²

• [₅₄Xe] 4f¹5d¹6s²

• [₅₄Xe] 4f³6s²

• [₅₄Xe] 4f³5d²

387.

The size of the iso-electronic species Cl^-, Ar and Ca²⁺ is affected by:

• nuclear charge

• Prinicpal quantum number of valence shell

• azimuthal quantum number of valence shell

• electron-electron interaction in the outer orbitals

Among the following species, the diamagnetic molecule is:

• B₂

• O₂

• CO

• NO

The element having greatest difference between its first and second ionization energies, is

• K

• Ca

• Ba

• Sc

The electronic configuration of Eu (Atomic no.63), Gd (Atomic no. 64) and Tb (Atomic no. 65) are

• [Xe]4f⁶ 5d¹ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹  6s² 

• [Xe] 4f⁶ 5d¹ 6s² , [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁸ 5d¹ 6s² 

• [Xe] 4f⁷  6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s² 

• [Xe] 4f⁷  6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s²