Chemistry

44.  (C) IO₃^- 

Iodide is oxidised to iodate.  

2KMnO₄ +  KI  + H₂O → 2KOH  +  2MnO₂ +  KIO₃

               iodide                                               iodate 

43.  (B) 3.87 B.M. 

Cr →  (Z = 24)

Cr3 +  →  (Z = 21)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s⁰

n  =  3 ( 3 unpaired electrons )

μ = $\sqrt[]{n(n+2)}$

μ = $\sqrt[]{3(3+2)}$

μ = $\sqrt[]{3\left(5\right)}$

μ = $\sqrt[]{15}$

=  3.87 B.M. 

42.  (D) They are chemically very reactive.

Interstitial compounds/alloys are substances that are formed when a small atom like carbon, hydrogen, boron, nitrogen can occupy space in their lattices. All the properties mentioned above are true for interstitial compounds except (D), they are chemically inert.

41.  (A) [Xe] 4f⁷ 5d¹ 6s²

Gadolinium belongs to the 4f series; it has atomic no.= 64. It has extra stability due to a half-filled 4f subshell.

Gd  (Z=64) ?   [Xe] 4f⁶ 5d² 6s² 

40.  (A) V₂O₅, Cr₂O₃

Oxides in the lower oxidation state are basic and in the higher oxidation state they are acidic. They are amphoteric in the intermediate oxidation state. Therefore, V₂O₅, Cr₂O₃ are amphoteric in nature.

39.  (A) 25

2MnO₄^-  +  5S^2-  + 16H⁺  → 2Mn²⁺  +  5S  + H₂O

From the reaction,

For 5 moles of S, two moles of KMnO₄ were required.

Therefore, for one  mole of S, the number of moles of KMnO₄ required will be = 25.

This is a Multiple Choice Questions as classified in NCERT Exemplar

43. Option (ii) 3,4- dimethyl hexane is correct since in selecting the longest continuous carbon chain both the ethyl groups are included while the third and fourth carbons have methyl groups as a substituent.

This is a Multiple Choice Questions as classified in NCERT Exemplar

42. Option (i) II > I > III is correct since in case (I), positively charged C is attached to two alkyl groups and is stabilized through  +I effect. In case (II), +R effect of - OCH3group stabilizes this carbocation. In case (III), - I effect of - OCH3 group destabilizes the carbocation.

Hence, the order of stability is given as: 

II > I >III.

This is a Multiple Choice Questions as classified in NCERT Exemplar

41. Option (ii) Partition is correct since partition chromatography is based on the principle of continuous differential partitioning of components of a mixture between a stationary and a mobile phase. Paper chromatography is a type of partition chromatography only.

This is a Multiple Choice Questions as classified in NCERT Exemplar

40. Option (iv)

Thin layer chromatography is correct since thin layer chromatography is a method for analysing the mixtures by separating the components of the mixture. This technique can be used to determine the number of components in a mixture, the identity of compounds and the purity of compounds by observing the appearance of a product or the disappearance of a reactant. It can also be used to analyse the progress of a reaction.