Chemistry
- Which one is the wrong statement ? Answer: 3. The energy of 2s orbital is less than the energy of 2p orbital in case of Hydrogen like atoms. Key idea: in a hydrogen-like atom,... 1
- Mechanism of a hypothetical reaction X_2 + Y_2 → 2XY is given below :(i) X_2 → X + X (fast)(ii) X + Y_2 ⇌ XY + Y (slow)(iii) X + Y → XY (fast)The overall order of the reaction will be : Answer: 3. 1.5 Key idea: the rate law comes from the slow step; intermediates must be replaced using the fast equilibrium. Rate = k[X][Y₂] (... 1
- For a given reaction, Δ H = 35.5\ kJ\ mol^-1 and Δ S = 83.6\ JK^-1mol^-1. The reaction is spontaneous at : (Assume that Δ H and Δ S do not vary with temperature) Answer: 1. T > 425 K Key idea: a reaction is spontaneous when Δ G = Δ H - TΔ S < 0 . For Δ G<0 : T > Δ H/Δ S . T > dfrac35.5×10³\ mathrmJ mo... 1
- The element Z = 114 has been discovered recently. It will belong to which of the following family/group and electronic configuration ? Answer: 1. Carbon family, [Rn] 5f¹⁴6d¹⁰7s²7p² Key idea: element 114 lies in the same group as Pb (Z = 82), one period lower, so its outer sh... 1
- Pick out the correct statement with respect to [Mn(CN)_6]^3- : Answer: 2. It is d²sp³ hybridised and octahedral Key idea: cyanide is a strong-field ligand, which pairs the d electrons. In [Mn(CN)₆]³⁻ , M... 1
- An example of a sigma bonded organometallic compound is : Answer: 1. Grignard's reagent Key idea: in a sigma-bonded organometallic compound, a metal-carbon sigma bond is present. Grignard's reagent,... 1
- Which one of the following statements is not correct ? Answer: 1. The value of equilibrium constant is changed in the presence of a catalyst in the reaction at equilibrium. Key idea: a catalyst c... 1
- The equilibrium constants of the following are :N_2 + 3H_2 ⇌ 2NH_3 K_1N_2 + O_2 ⇌ 2NO K_2H_2 + 1/2O_2 → H_2O K_3The equilibrium constant (K) of the reaction : 2NH_3 + 5/2O_2 K⇌ 2NO + 3H_2O, will be : Answer: 1. K₂K₃³/K₁ Key idea: combine reactions; reversing gives 1/K , multiplying by n gives Kⁿ , adding gives the product of K values. Tar... 1
- A 20 litre container at 400 K contains CO_2(g) at pressure 0.4 atm and an excess of SrO (neglect the volume of solid SrO). The volume of the container is now decreased by moving the movable piston fitted in the container. The maximum volume of the co… Answer: 4. 5 litre Key idea: for SrCO₃(s)⇌ SrO(s)+CO₂(g) , K_p = p_(CO_2) at equilibrium, so the maximum pressure of CO₂ is 1.6 atm. Initial... 1
- With respect to the conformers of ethane, which of the following statements is true ? Answer: 3. Both bond angles and bond length remains same Key idea: conformers differ only by rotation about the C-C single bond. Staggered a... 1
- Identify A and predict the type of reaction. [Reactant: 3-bromoanisole (benzene ring with OCH3 and Br meta to each other) with NaNH2 gives A] Answer: 4. [structure: 3-aminoanisole (OCH3 and NH2 meta)] and substitution reaction Key idea: aryl halide with NaNH₂ reacts through a benzy... 1
- The correct increasing order of basic strength for the following compounds is : [(I) aniline, (II) 4-nitroaniline, (III) 4-methylaniline] Answer: 3. II < I < III Key idea: basic strength depends on how available the lone pair on N is. -CH₃ is electron-donating (+I, hyperconjuga... 1
- Mixture of chloroxylenol and terpineol acts as : Answer: 1. antiseptic Key idea: a chloroxylenol and terpineol mixture is the well-known disinfectant Dettol. It is used on skin and wounds t... 1
- Which of the following is a sink for CO ? Answer: 1. Micro organisms present in the soil Key idea: CO is removed from air mainly by soil micro-organisms. Certain soil bacteria and fu... 1
- It is because of inability of ns^2 electrons of the valence shell to participate in bonding that : Answer: 4. Sn²⁺ is reducing while Pb⁴⁺ is oxidising Key idea: the inert pair effect makes the +2 state more stable than +4 in heavy group 14... 1
- Name the gas that can readily decolourise acidified KMnO_4 solution : Answer: 1. SO₂ Key idea: KMnO₄ is decolourised by a reducing gas. SO₂ is a reducing agent: 5SO₂ + 2MnO₄^- + 2H₂O → 5SO₄²⁻ + 2Mn²⁺ + 4H^+ . P... 1
- HgCl_2 and I_2 both when dissolved in water containing I^- ions the pair of species formed is : Answer: 2. HgI₄²⁻, I₃^- Key idea: HgI₂ dissolves in excess I^- and I₂ dissolves in I^- by complex formation. HgCl₂ + 2I^-→ HgI₂ (red precipi... 1
- Which of the following is dependent on temperature ? Answer: 1. Molarity Key idea: a concentration term that uses volume changes with temperature, because volume changes. Molarity = moles of so... 1
- If the E^°_cell for a given reaction has a negative value, which of the following gives the correct relationships for the values of Δ G^° and K_eq? Answer: 4. Δ G^° > 0 ; K_eq < 1 Key idea: Δ G^°=-nFE^°_cell=-RTln K . If E^°_cell<0 , then Δ G^°>0 , so ln K<0 and K_eq<1 . The reaction is... 1
- How many electrons can fit in the orbital for which n = 3 and l = 1? Answer: 4. 2 Key idea: one orbital holds at most 2 electrons (Pauli principle). n=3,l=1 is the 3p subshell, which has 3 orbitals (6 electron... 1
- The correct corresponding order of names of four aldoses with configuration given below [four Fischer projections] respectively, is Answer: 3. D-erythrose, D-threose, L-erythrose, L-threose Key idea: D/L is decided by the OH on the lowest chiral carbon (right = D). Erythr... 1
- In calcium fluoride, having the fluorite structure, the coordination numbers for calcium ion (Ca^2+) and fluoride ion (F^-) are Answer: 2. 8 and 4 Key idea: in the fluorite structure, Ca²⁺ forms an fcc lattice and F^- occupies all tetrahedral holes. Each F^- is surrou... 1
- Which one of the following compounds shows the presence of intramolecular hydrogen bond? Answer: 2. Cellulose Key idea: the key gives cellulose; the stem is partly unreadable, so the answer follows the key. HCN, concentrated acet... 1
- The decomposition of phosphine [obscured] on tungsten at low pressure is a [obscured] reaction. It is because the Answer: 4. rate is proportional to the surface coverage Key idea: on a metal surface at low pressure the surface is not saturated, so the ra... 1