#neet
- Which of the following has longest C-O bond length ? (Free C-O bond length in CO is 1.128\ .) Answer: 3. [Fe(CO)₄]²⁻ Key idea: in metal carbonyls, back bonding from metal d orbitals into the CO π^* orbital weakens the C-O bond and len... 1
- The pressure of H_2 required to make the potential of H_2 - electrode zero in pure water at 298 K is : Answer: 1. 10⁻¹⁴ atm Key idea: for the half cell 2H^++2e^-→ H₂ , the Nernst equation is E=0-0.059/2logfracP_(H_2)[H^+]² In pure water [H^+]=... 1
- The addition of a catalyst during a chemical reaction alters which of the following quantities ? Answer: 4. Activation energy Key idea: a catalyst provides a different path with a lower activation energy. It does not change the state fun... 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
- Which is the correct statement for the given acids ? Answer: 2. Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid. Key idea: only the P-OH hydrogens are acidic. Phos... 1
- Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct ? Assume that the temperature is constant at 25°C. (Given, Vapour Pressure Data at 25°C, benzene = 12.8 kPa, tol… Answer: 1. The vapour will contain a higher percentage of benzene. Key idea: the component with the higher vapour pressure is more volatile... 1
- The correct statement regarding the comparison of staggered and eclipsed conformations of ethane, is : Answer: 4. The staggered conformation of ethane is more stable than eclipsed conformation, because staggered conformation has no torsional s... 1
- The reaction[cyclopentanol, then NaH giving sodium cyclopentoxide, then Me-I giving methyl cyclopentyl ether; scheme shown in figure]can be classified as : Answer: 1. Williamson ether synthesis reaction Key idea: an alcohol is converted by a strong base (NaH) into an alkoxide, which then attacks... 1
- When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is V/4. The threshold wavelength for the metallic surface i… Answer: 4. 3λ Key idea: eV=hc/λ-hc/λ₀ . eV=hc/λ-φ and eV/4=hc/2λ-φ . Subtracting: 3/4eV=hc/2λ⇒ eV=2hc/3λ . φ=hc/λ-2hc/3λ=hc/3λ , so λ₀=3λ . 1
- A gas is compressed isothermally to half its initial volume. The same gas is compressed separately through an adiabatic process until its volume is again reduced to half. Then : Answer: 2. Compressing the gas through adiabatic process will require more work to be done. Key idea: compare areas under the P-V curves. Fo... 1
- A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from th… Answer: 4. 3 : 2 Key idea: balance length is proportional to the emf in the circuit. Supporting: ε₁+ε₂∝50 ; opposing: ε₁-ε₂∝10 . So ε₁∝30 an... 1
- A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance : Answer: 4. 54.0 cm Key idea: the objective forms an image of the nearby object; the eyepiece must focus on that image (final image at infini... 1
- Two non-mixing liquids of densities ρ and nρ (n > 1) are put in a container. The height of each liquid is h. A solid cylinder of length L and density d is put in this container. The cylinder floats with its axis vertical and length pL (p < 1) in the… Answer: 4. \1+(n-1)p\ρ Key idea: weight of cylinder equals total buoyant force. Length pL is in the denser liquid ( nρ ); remaining (1-p)L i... 1
- To get output 1 for the following circuit, the correct choice for the input is : Answer: 4. A = 1, B = 0, C = 1 Key idea: from the circuit, Y=(A+B)· C : A and B go to an OR gate, and its output goes to an AND gate with C.... 1
- A piece of ice falls from a height h so that it melts completely. Only one - quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of h is : [Latent heat of ice is 3.4×10^5 J/kg… Answer: 3. 136 km Key idea: loss in potential energy mgh becomes heat; one-quarter of it melts the ice. 1/4mgh=mL⇒ h=4L/g=dfrac4×3.4×10⁵10=1... 1
- The ratio of escape velocity at earth (v_e) to the escape velocity at a planet (v_p) whose radius and mean density are twice as that of earth is : Answer: 2. 1 : 2√(2) Key idea: v_e=√(2GM/R)=R√(8π Gρ/3) , so v_e∝ Rsqrtρ . Planet: radius 2R , density 2ρ , so v_p=v_e×2×sqrt2=2sqrt2 v_e .... 1
- If the magnitude of sum of two vectors is equal to the magnitude of difference of the two vectors, the angle between these vectors is : Answer: 2. 90^° Key idea: |vec A+vec B|²=A²+B²+2ABcosθ and |vec A-vec B|²=A²+B²-2ABcosθ . Setting them equal gives 4ABcosθ=0 , so cosθ=0 and... 1
- Given the value of Rydberg constant is 10^7\ m^-1, the wave number of the last line of the Balmer series in hydrogen spectrum will be : Answer: 3. 0.25×10⁷\ m⁻¹ Key idea: barν=R(dfrac12²-dfrac1n²) ; the last Balmer line has n→∞ . barν=R/4=10⁷/4=0.25×10⁷\ m⁻¹ . 1
- A body of mass 1 kg begins to move under the action of a time dependent force F = (2t i + 3t^2 j) N, where i and j are unit vectors along x and y axis. What power will be developed by the force at the time t ? Answer: 4. (2t³ + 3t⁵) W Key idea: power P=vec F·vec v ; find vec v by integrating vec a=vec F/m . vec a=2that i+3t²hat j (m = 1 kg), so vec... 1
- An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf V = 10 340 t. The power loss in A.C. circuit is : Answer: 1. 0.51 W Key idea: average power P=I_rms²R , with I_rms=V_rms/Z . X_L=ω L=340×0.02=6.8\ Ω ; X_C=dfrac1ω C≈58.8\ Ω . Z=√(40²+52²)=√(... 1
- If the velocity of a particle is v = At + Bt^2, where A and B are constants, then the distance travelled by it between 1s and 2s is : Answer: 3. 3/2A + 7/3B Key idea: distance is the integral of speed over time (here v≥0 ). s=∫₁²(At+Bt²)dt=A4-1/2+B8-1/3=3/2A+7/3B . 1
- A long solenoid has 1000 turns. When a current of 4A flows through it, the magnetic flux linked with each turn of the solenoid is 4×10^-3 Wb. The self-inductance of the solenoid is : Answer: 4. 1 H Key idea: L=Nφ/I , where φ is the flux per turn. L=dfrac1000×4×10⁻³4=1 H. 1
- A small signal voltage V(t) = V_0 ω t is applied across an ideal capacitor C : Answer: 2. Over a full cycle the capacitor C does not consume any energy from the voltage source. Key idea: in an ideal capacitor, current l... 1
- Match the corresponding entries of column 1 with column 2. [Where m is the magnification produced by the mirror]Column 1: (A) m = -2; (B) m = -1/2; (C) m = +2; (D) m = +1/2Column 2: (a) Convex mirror; (b) Concave mirror; (c) Real image; (d) Virtual i… Answer: 1. A → b and c; B → b and c; C → b and d; D → a and d Key idea: real images have negative m (inverted); virtual images have positive... 1