#neet
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- An oxygen cylinder of volume 30 litre has 18.20 moles of oxygen. After some oxygen is withdrawn from the cylinder, its gauge pressure drops to 11 atmospheric pressure at temperature 27^°C. The mass of the oxygen withdrawn from the cylinder is nearly… Answer: 3. 0.116 kg Key idea: use PV=nRT for the gas left, then subtract from the initial moles. The gauge pressure must be converted to abs... 1
- In some appropriate units, time (t) and position (x) relation of a moving particle is given by t = x^2 + x. The acceleration of the particle is Answer: 2. -2/(2x+1)³ Key idea: differentiate t(x) to get velocity, then use a=v dv/dx . dt/dx=2x+1⇒ v=dx/dt=1/2x+1 a=vdv/dx=1/2x+1·(-2/(2x+... 1
- To an ac power supply of 220 V at 50 Hz, a resistor of 20 Ω, a capacitor of reactance 25 Ω and an inductor of reactance 45 Ω are connected in series. The corresponding current in the circuit and the phase angle between the current and the voltage is,… Answer: 2. 7.8 A and 45^° Key idea: in a series LCR circuit, Z=√(R²+(X_L-X_C)²) and tanφ=X_L-X_C/R . X_L-X_C=45-25=20\ Ω, Z=√(20²+20²)=20sqr... 1