Carbon cannot reduce Fe₂O₃ to Fe at a temperature below 983 K because

• free energy change for the formation of CO is more negative than that of Fe₂O₃

• CO is thermodynamically more stable than Fe₂O₃

• carbon has higher affinity towards oxygen than iron

• iron has higher affinity towards oxygen than carbon

Which one of the following is a covalent crystal?

• Rock salt

• Ice

• Quartz

• Dry ice

The percentage of p-character of the hybrid orbitals in graphite and diamond are respectively

• 50 and 75

• 67 and 75

• 33 and 75

• 33 and 25

An alkali metal hydride (NaH) reacts with diborane in. A to give a tetrahedral compound B which is extensively used as reducing agent in organic synthesis. The compounds A and B respectively are

• C₂H₆ and C₂H₅Na

• CH₃COCH₃ and B₃N₃H₆

• C₆H₆ and NaBH₄

• (C₂H₅)₂O and NaBH₄

The correct statement is

• BF₃ is the strongest Lewis acid among the other boron halides

• BI₃ is the weakest Lewis acid among the other boron halides

• there is maximum pπ- pπ back boinding in BF₃

• there is minimum pπ- pπ back boinding in BF₃

The hybridisation of C in diamond, graphite and ethyne is in the order.

• sp³, sp, sp²

• sp³, sp², sp

• sp, sp², sp³

• sp², sp³, sp

The formula of mineral borax is :

• Na₂B₄O₇

• Na₂B₄O₇.4H₂O

• Na₂B₄O₇.5H₂O

• Na₂B₄O₇.10H₂O

The electronegativities of C, N, Si and P are in the order of

• P < Si<C < N

• Si <P < C<N

• P < Si < N < C

• Si <P < N <C

79.

Addition of mineral acid to an aqueous solution of borax, the following compound is formed

• pyroboric acid

• boron hydride

• meta boric acid

• orthoboric acid

Which of the following equations correctly represents the standard heat of formation ($∆{\mathrm{H}}_{\mathrm{f}}^{°}$H) of methane ?

• C (diamond) + 4H (g) → CH₄ (g)

• C (diamond) + 2H₂ (g) → CH₄ (g)

• C (graphite) + 2H₂ (g) → CH₄ (g)

• C (graphite) + 4H (g) → CH₄ (g)