NEET UG
- 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
- A full wave rectifier circuit with diodes (D_1) and (D_2) is shown in the figure. If input supply voltage V_in = 220(100π t) volt, then at t = 15 msec Answer: 1. D₁ is forward biased, D₂ is reverse biased or 2. D₁ is reverse biased, D₂ is forward biased Key idea: in a centre-tapped full-wav... 1
- The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at 22.5^° from the polarization axis of one of the polaroid, is (I_0 is the intensity of polarised light after passing through the first polaroid): Answer: 3. I₀/8 Key idea: apply Malus's law, I=I₀cos²θ , at each polaroid. The middle sheet is at 22.5^° to the first, and 90^°-22.5^°=67.5^... 1
- Two identical point masses P and Q, suspended from two separate massless springs of spring constants k_1 and k_2, respectively, oscillate vertically. If their maximum speeds are the same, the ratio (A_Q/A_P) of the amplitude A_Q of mass Q to the ampl… Answer: 4. √(k₁/k₂) Key idea: the maximum speed in SHM is v_max=Aω=A√(k/m) . Masses are identical and v_max is the same, so A_P√(k₁)=A_Q√(k₂... 1
- A pipe open at both ends has a fundamental frequency f in air. The pipe is now dipped vertically in a water drum to half of its length. The fundamental frequency of the air column is now equal to : Answer: 2. f Key idea: an open pipe of length L has fundamental f=v/2L ; a pipe closed at one end of length l has fundamental v/4l . Dipping... 1
- A physical quantity P is related to four observations a, b, c and d as follows:P = a^3b^2 / c√(d)The percentage errors of measurement in a, b, c and d are 1%, 3%, 2%, and 4% respectively. The percentage error in the quantity P is Answer: 3. 13% Key idea: for P=a³b²/csqrt d , the maximum percentage error is the sum of (power × percentage error) of each quantity. Δ P/P×... 1
- Two gases A and B are filled at the same pressure in separate cylinders with movable pistons of radius r_A and r_B, respectively. On supplying an equal amount of heat to both the systems reversibly under constant pressure, the pistons of gas A and B… Answer: 2. 3/4 Key idea: at constant pressure, Q=Δ U+W with W=pΔ V . The heat supplied and Δ U are the same for both gases, so W is equal. W... 1
- A model for quantized motion of an electron in a uniform magnetic field B states that the flux passing through the orbit of the electron is n(h/e) where n is an integer, h is Planck's constant and e is the magnitude of electron's charge. According to… Answer: 2. he/2π m Key idea: the electron moves in a circle in the field, and the given flux quantization fixes the orbit area. From evB=mv²... 1
- A particle of mass m is moving around the origin with a constant force F pulling it towards the origin. If Bohr model is used to describe its motion, the radius r of the n^th orbit and the particle's speed v in the orbit depend on n as Answer: 3. r ∝ n^(2/3);\ v ∝ n^(1/3) Key idea: apply Newton's second law with the constant force as the centripetal force, together with Boh... 1
- A constant voltage of 50 V is maintained between the points A and B of the circuit shown in the figure. The current through the branch CD of the circuit is : Answer: 2. 2.0 A Key idea: C and D are joined by a wire, so they are at the same potential. The circuit becomes two parallel pairs in series... 1