Chemistry
- Among the following, which one is a wrong statement? Answer: 2. SeF₄ and CH₄ have same shape. Key idea: compare VSEPR shapes. SO₂ has pπ - dπ bonding: correct. SeF₄ is see-saw (4 bond pairs + 1... 1
- Which of the following pairs of ions is isoelectronic and isostructural? Answer: Dropped in the official answer key: full marks to every candidate Key idea: compare total electrons and shape. CO₃²⁻ and NO₃^- : 32... 1
- The correct geometry and hybridization for XeF_4 are Answer: 3. square planar, sp³d² Key idea: Xe in XeF₄ has 4 bond pairs and 2 lone pairs. Steric number 6 gives sp³d² hybridisation and an oct... 1
- The suspension of slaked lime in water is known as Answer: 2. milk of lime Key idea: Ca(OH)₂ is only sparingly soluble in water. A suspension of slaked lime in water looks milky, so it is cal... 1
- The solubility of AgCl (s) with solubility product 1.6×10^-10 in 0.1 M NaCl solution would be Answer: 1. 1.6×10⁻⁹ M Key idea: the common ion Cl^- from NaCl suppresses the solubility of AgCl. Let solubility be s . [Ag^+]=s , [Cl^-]≈ 0.... 1
- Boric acid is an acid because its molecule Answer: 2. accepts OH^- from water releasing proton Key idea: boric acid is a Lewis acid, not a proton donor. Boron in B(OH)₃ has an empty p... 1
- AlF_3 is soluble in HF only in presence of KF. It is due to the formation of Answer: 1. K₃[AlF₆] Key idea: AlF₃ is covalent and insoluble; extra F^- from KF forms a soluble complex. AlF₃+3KF→ K₃[AlF₆] The stable hexaf... 1
- Which of the following fluoro-compounds is most likely to behave as a Lewis base? Answer: 1. PF₃ Key idea: a Lewis base needs a lone pair to donate. PF₃ : P has a lone pair, so it can act as a donor. CF₄ : no lone pair and... 1
- Hot concentrated sulphuric acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidizing behaviour? Answer: 3. CaF₂ + H₂SO₄ → CaSO₄ + 2HF Key idea: oxidising behaviour means H₂SO₄ is reduced (S goes from +6 to +4 as SO₂ ). Options 1, 2, 4:... 1
- In context with beryllium, which one of the following statements is incorrect? Answer: 2. Its salts rarely hydrolyze. Key idea: Be is small and highly polarising, so its salts hydrolyse readily. Be forms Be₂C (carbide):... 1
- The number of electrons delivered at the cathode during electrolysis by a current of 1 ampere in 60 seconds is (charge on electron = 1.60×10^-19 C) Answer: 2. 3.75×10²⁰ Key idea: charge Q=It , and number of electrons =Q/e . Q=1×60=60\ C n=frac601.60×10⁻¹⁹=3.75×10²⁰ Option 4 ( 6×10²³ ) is... 1
- Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because Answer: 3. zinc has higher negative electrode potential than iron Key idea: a more electropositive metal can protect a less electropositive... 1
- Which one of the following is incorrect for ideal solution? Answer: 3. Δ G_mix=0 Key idea: an ideal solution has no net interaction change on mixing, and mixing is spontaneous. Δ H_mix=0 and Δ U_mix=0... 1
- Suppose the elements X and Y combine to form two compounds XY_2 and X_3Y_2. When 0.1 mole of XY_2 weighs 10 g and 0.05 mole of X_3Y_2 weighs 9 g, the atomic weights of X and Y are Answer: 4. 40, 30 Key idea: molar mass = mass / moles, then form two equations in the atomic masses X and Y. XY₂ : M=10/0.1=100⇒ X+2Y=100 X₃... 1
- The correct statement regarding RNA and DNA, respectively is : Answer: 2. The sugar component in RNA is ribose and the sugar component in DNA is 2'-deoxyribose. Key idea: RNA has the sugar D-ribose and D... 1
- Which one given below is a non-reducing sugar ? Answer: 4. Sucrose Key idea: a sugar is non-reducing when both anomeric carbons are tied up in the glycosidic bond, leaving no free hemiacet... 1
- For the following reactions :(a) CH_3CH_2CH_2Br + KOH → CH_3CH=CH_2 + KBr + H_2O(b) (CH3)2CHBr + KOH -> (CH3)2CHOH + KBr (structures shown in figure)(c) cyclohexene + Br_2 -> 1,2-dibromocyclohexane (structures shown in figure)Which of the following s… Answer: 2. (a) is elimination, (b) is substitution and (c) is addition reaction. Key idea: identify what happens to the substrate. (a) CH₃CH... 1
- The correct statement regarding the basicity of arylamines is : Answer: 1. Arylamines are generally less basic than alkylamines because the nitrogen lone-pair electrons are delocalized by interaction with... 1
- At 100°C the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If K_b = 0.52, the boiling point of this solution will be : Answer: 1. 101°C Key idea: use the lowering of vapour pressure to get the mole fraction, and then the boiling point elevation. At 100°C pure... 1
- Which of the following biphenyls is optically active ? Answer: 2. [structure shown in figure] Key idea: a biphenyl is optically active (shows atropisomerism) only if rotation about the central bo... 1
- The pair of electron in the given carbanion, CH_3C C^, is present in which of the following orbitals ? Answer: 4. sp Key idea: the carbanion carbon in CH₃Cequiv C^- is triply bonded to another carbon, so it has 2 regions of electron density an... 1
- Two electrons occupying the same orbital are distinguished by : Answer: 4. Spin quantum number Key idea: two electrons in the same orbital have the same n, l and m. By the Pauli exclusion principle they m... 1
- The ionic radii of A^+ and B^- ions are 0.98×10^-10 m and 1.81×10^-10 m. The coordination number of each ion in AB is : Answer: 1. 6 Key idea: the radius ratio decides the coordination number. r_+/r_-=0.98/1.81=0.54 This lies in 0.414-0.732, which means octahe... 1
- Match the compounds given in column I with the hybridisation and shape given in column II and mark the correct option.Column I: (a) XeF_6; (b) XeO_3; (c) XeOF_4; (d) XeF_4Column II: (i) distorted octahedral; (ii) square planar; (iii) pyramidal; (iv)… Answer: 1. (i) (iii) (iv) (ii) Key idea: use VSEPR for each xenon compound. XeF₆ : sp³d³ , 6 bond pairs + 1 lone pair, distorted octahedral... 1