In borax the number of B-O-B links and B-OH bonds present are, respectively

• five and four

• four and five

• three and four

• five and five

The stable bivalency of Pb and trivalency of Bi is

• due to d contraction in Pb and Bi

• due to relativistic contraction of the 6s orbitals of Pb and Bi, leading to inert pair effect

• due to screening effec

• due to attainment of noble liquid configuration

Which of the following is correct?

• Radius of Ca²⁺ <Cl^- < S^2-

• Radius of  <Cl^- < S^2- < Ca²⁺

• Radius of S^2-= Cl^-= Ca²⁺

• Radius of Ca²⁺ >Cl^- > S^2-

Which one of the following has the lowest ionisation energy?

• 1s², 2s², 2p⁶

• 1s², 2s², 2p⁶, 3s¹

• 1s², 2s², 2p⁵

• 1s², 2s², 2p³

If the first ionization energy of H atom is 13.6 eV, then the second ionization energy of He atom is

• 27.2 eV

• 40.8 eV

• 54.4 eV

• 108.8 eV

26.

How many unpaired electrons are present in Ni²⁺ cation? (Z = 28)

• 0

• 2

• 4

• 6

An oxide of a non-metal has the following properties

(i) It acts both as proton donor as well as proton acceptor

(ii) It reacts readily with basic and acidic oxides

(iii) It oxidies Fe at its boiling point. The oxide maybe

• P₂O₅

• SiO₂

• H₂O

• CO₂

Consider the following changes

M(s) → M(g)                ... (1)
M(g) → M²⁺(g) + 2e^-    ...(2)
Mg) → M⁺(g) + e^-         ...(3)
M(g) → M²⁺(g) + e^-      ...(4)
M(g) → M²⁺ (g) + 2e^-   ...(5)
The second ionisation energy of M could be determined from the energy values associated with 

• 1 + 2 + 4

• 2 + 3 - 4

• 1 + 5 - 3

• 5 - 3

If the ionisation energy and electron affinity of an element are 275 and 86 kcal mol^-1 respectively, then the electronegativity of the element on the Mulliken scale is

• 2.8

• 0.0

• 4.0

• 2.6

Which of the following has the maximum number of unpaired d-electrons?

• Fe²⁺

• Cu⁺

• Zn

• Ni³⁺