Chemistry
- Among the following, choose the ones with equal number of atoms.A. 212 g of Na_2CO_3 (s) [molar mass = 106 g]B. 248 g of Na_2O (s) [molar mass = 62 g]C. 240 g of NaOH (s) [molar mass = 40 g]D. 12 g of H_2 (g) [molar mass = 2 g]E. 220 g of CO_2(g) [mo… Answer: 2. A, B, and D only Key idea: number of atoms = moles × atoms per formula unit × N_A . A: 212 g = 2 mol × 6 = 12 mol atoms. B: 248 g... 1
- Among the given compounds I-III, the correct order of bond dissociation energy of C-H bond marked with * is : Answer: 1. II > I > III Key idea: the more s-character in the carbon, and the less stable the radical left behind, the stronger the C-H bond... 1
- Total number of possible isomers (both structural as well as stereoisomers) of cyclic ethers of molecular formula C_4H_8O is : Answer: 3. 10 Key idea: list all rings of formula C₄H₈O containing O, and count enantiomers/cis-trans. Oxolane (THF): 1. Oxetane with a meth... 1
- Energy and radius of first Bohr orbit of He^+ and Li^2+ are[Given R_H = 2.18×10^-18 J, a_0 = 52.9 pm] Answer: 1. E_n(mathrmLi²⁺) = -19.62×10⁻¹⁸ J; r_n(mathrmLi²⁺) = 17.6 pm; E_n(He^+) = -8.72×10⁻¹⁸ J; r_n(He^+) = 26.4 pm Key idea: for hydroge... 1
- The ratio of the wavelengths of the light absorbed by a Hydrogen atom when it undergoes n=2 → n=3 and n=4 → n=6 transitions, respectively, is Answer: 4. 1/4 Key idea: absorbed wavelength is inversely proportional to the energy gap, 1/λ∝(1/n₁²-1/n₂²) . For 2→3 : 1/4-1/9=5/36 , so λ₁... 1
- Given below are two statements :Statement I : A hypothetical diatomic molecule with bond order zero is quite stable.Statement II : As bond order increases, the bond length increases.In the light of the above statements, choose the most appropriate an… Answer: 2. Both Statement I and Statement II are false Key idea: bond order measures net bonding; it links to stability and bond length. Sta... 1
- If the half-life (t_1/2) for a first order reaction is 1 minute, then the time required for 99.9% completion of the reaction is closest to : Answer: 4. 10 minutes Key idea: first order: k=frac0.693t_(1/2) and t=2.303/kloga/a-x . k=0.693\ mathrmmin⁻¹ . 99.9% complete: a/a-x=1000 ,... 1
- Which of the following statements are true?A. Unlike Ga that has a very high melting point, Cs has a very low melting point.B. On Pauling scale, the electronegativity values of N and Cl are not the same.C. Ar, K^+, Cl^-, Ca^2+, and S^2- are all isoel… Answer: 2. C and E only Key idea: check each statement separately. A false: gallium melts at only about 30 °C, so it does not have a very hi... 1
- Which among the following electronic configurations belong to main group elements?A. [Ne]3s^1 B. [Ar]3d^3 4s^2 C. [Kr]4d^105s^2 5p^5 D. [Ar]3d^104s^1 E. [Rn]5f^0 6d^2 7s^2Choose the correct answer from the option given below : Answer: 2. A and C only Key idea: main group elements are s- and p-block elements; d-block elements have d electrons being filled. A: [Ne]3s... 1
- Which of the following are paramagnetic?A. [NiCl_4]^2- B. Ni(CO)_4 C. [Ni(CN)_4]^2- D. [Ni(H_2O)_6]^2+ E. Ni(PPh_3)_4Choose the correct answer from the options given below: Answer: 3. A and D only Key idea: paramagnetic means unpaired electrons. A: mathrm[NiCl₄]²⁻ , mathrmNi²⁺ d⁸, weak field Cl⁻, tetrahedral sp³... 1
- The correct order of the wavelength of light absorbed by the following complexes is,A. [Co(NH_3)_6]^3+ B. [Co(CN)_6]^3- C. [Cu(H_2O)_4]^2+ D. [Ti(H_2O)_6]^3+Choose the correct answer from the options given below: Answer: 2. B < A < D < C Key idea: the larger the crystal field splitting Δ , the higher the energy absorbed and the shorter the wavelength.... 1
- Out of the following complex compounds, which of the compound will be having the minimum conductance in solution? Answer: 1. [Co(NH₃)₃Cl₃] or 2. [Co(NH₃)₄Cl₂] Key idea: conductance in solution depends on the number of ions produced; a non-electrolyte giv... 1
- Phosphoric acid ionizes in three steps with ionization constant values K_a_1, K_a_2 and K_a_3, respectively, while K is the overall ionization constant. Which of the following statements are true?A. K = K_a_1 + K_a_2 + K_a_3B. H_3PO_4 is a stronger a… Answer: 4. A, B and C only Key idea: overall K=K_(a_1)K_(a_2)K_(a_3) , and each successive ionization is harder. A true: taking logs, log K=... 1
- Which one of the following reactions does NOT give benzene as the product ? Answer: 4. benzenediazonium chloride with H₂O , warm Key idea: identify the product of each reaction. Sodium benzoate + soda lime, heat: dec... 1
- Predict the major product 'P' in the following sequence of reactions -(i) HBr, benzoyl peroxide; (ii) KCN; (iii) Na(Hg)/C_2H_5OH -> P (Major), starting from 1-methylcyclopentene Answer: 1. methylcyclopentane with CH₂NH₂ (see figure) Key idea: HBr with peroxide adds anti-Markovnikov, KCN replaces Br by CN, and Na(Hg)/... 1
- Given below are two statements :Statement I : Like nitrogen that can form ammonia, arsenic can form arsine.Statement II : Antimony cannot form antimony pentoxide.In the light of the above statements, choose the most appropriate answer from the option… Answer: 3. Statement I is correct but Statement II is incorrect Key idea: group 15 elements form hydrides EH₃ and oxides E₂O₅ . Statement I... 1
- Match List I with List IIList I (Ion): A. Co^2+ B. Mg^2+ C. Pb^2+ D. Al^3+List II (Group Number in Cation Analysis): I. Group-I II. Group-III III. Group-IV IV. Group-VIChoose the correct answer from the options given below : Answer: 2. A-III, B-IV, C-I, D-II Key idea: recall the group of each cation in qualitative analysis. mathrmPb²⁺ : Group I (precipitated as c... 1
- If the molar conductivity (_m) of a 0.050 mol L^-1 solution of a monobasic weak acid is 90 S cm^2 mol^-1, its extent (degree) of dissociation will be[Assume ^°_+ = 349.6 S cm^2 mol^-1 and ^°_- = 50.4 S cm^2 mol^-1.] Answer: 3. 0.225 Key idea: α=Lambda_m/Lambda^°_m for a weak electrolyte. Lambda^°_m=349.6+50.4=400 S cm² mol⁻¹. α=90/400=0.225 . Option (3). 1
- Consider the following compounds : KO_2, H_2O_2 and H_2SO_4.The oxidation states of the underlined elements in them are, respectively, Answer: 1. +1, -1, and +6 Key idea: assign oxidation states from known charges. KO₂ is potassium superoxide, K^+ and O₂^- : K = +1. H₂O₂ is... 1
- Dalton's Atomic theory could not explain which of the following? Answer: 4. Law of gaseous volume Key idea: Dalton's theory was about atoms combining in fixed whole-number ratios, with no concept of gas vo... 1
- Which one of the following compounds can exist as cis-trans isomers? Answer: 4. 1,2-Dimethylcyclohexane Key idea: cis-trans isomerism needs a double bond with different groups on each carbon, or a ring with tw... 1
- Identify the correct answer. Answer: 1. Three canonical forms can be drawn for CO₃²⁻ ion. Key idea: check each statement. mathrmCO₃²⁻ : three equivalent canonical forms.... 1
- The rate of a reaction quadruples when temperature changes from 27^°C to 57^°C. Calculate the energy of activation.Given R = 8.314 J K^-1 mol^-1, log 4 = 0.6021 Answer: 2. 38.04 kJ/mol Key idea: logk₂/k₁=E_a/2.303RT₂-T₁/T₁T₂ . T₁=300 K, T₂=330 K, k₂/k₁=4 . E_a=2.303×8.314×0.6021×300×330/30≈38046\ J/m... 1
- The work done during reversible isothermal expansion of one mole of hydrogen gas at 25^°C from pressure of 20 atmosphere to 10 atmosphere is:(Given R = 2.0 cal K^-1 mol^-1) Answer: 3. - 413.14 calories Key idea: for reversible isothermal expansion, w=-2.303 nRTlogP₁/P₂ (work done by the gas is negative in this c... 1