291.

Among the following, the pair in which the two species are not isostructural, is

• SiF₄ and SF₄

• IO${}_3^{-}$ and XeO₃

• BH${}_4^{-} \mathrm{and} {\mathrm{NH}}_4^{+}$

• PF${}_6^{-}$ and SF₆

The helical structure of protein is stabilized by

• dipeptide bond

• hydrogen bonds

• ether bonds

• peptide bonds

The dipole moment of HBr is 1.6 × 10^-30 cm and inter-atomic spacing is 1 Å. The % ionic character of HBr is

• 7

• 10

• 15

• 27

The bond angle is smallest in

• H₂O

• H₂S

• BeCl₂

• N₂O

Valence bond theory of metallic bond was given by

• Dalton

• Drudel

• Fajan

• Pauling 

Which combination of atoms can form a polar covalent bond ?

• H and N

• H and Br

• N and N

• Na and Br

The bond length of H${}_2^{+}$, H${}_2^{-}$ and H₂ are in the following order

• H${}_2^{+}$ > H₂ > H${}_2^{-}$

• H₂ > ${\text{H}}_2^{+} > {\mathrm{H}}_2^{-}$

• H${}_2^{-}$ > H₂ > H${}_2^{+}$

• ${\mathrm{H}}_2^{-} > {\mathrm{H}}_2^{+}$ > H₂

The correct order of bond length is

• b > a > c > d

• a > b > c > d

• d > c > b > a

• c > d > b > a

Consider the following ions:

(i) Ni²⁺   (ii) Co²⁺  (iii) Cr²⁺   (iv) Fe³⁺

(Given, at. no. Cr = 24, Fe = 26, Co = 27, Ni = 28)

The correct order of magnetic moment of these ions is

• (i) < (ii) < (iii) < (iv)

• (iv) < (ii) < (iii) < (i)

• (i) < (iii) < (ii) < (iv)

• (iii) < (iv) < (ii) < (i)

Geometry of methyl free radical is

• pyramidal

• planar

• tetrahedral

• linear