#neet
- Which one is an example of heterogenous catalysis? Answer: 1. Combination between dinitrogen and dihydrogen to form ammonia in the presence of finely divided iron. Key idea: In heterogeneous... 1
- Which one of the following statements is correct? Answer: 2. The daily requirement of Mg and Ca in the human body is estimated to be 0.2 - 0.3 g. Key idea: Recall the biological roles of Mg... 1
- Weight (g) of two moles of the organic compound, which is obtained by heating sodium ethanoate with sodium hydroxide in presence of calcium oxide is : Answer: 3. 32 Key idea: Sodium ethanoate heated with soda lime (NaOH + CaO) undergoes decarboxylation to give an alkane with one carbon fewe... 1
- The element expected to form largest ion to achieve the nearest noble gas configuration is : Answer: 4. N Key idea: For isoelectronic ions (all 10 electrons), the one with the lowest nuclear charge is the largest. The ions are Na^+ (... 1
- The correct order of energies of molecular orbitals of N_2 molecule, is : Answer: 2. σ 1s<σ^* 1s<σ 2s<σ^* 2s<(π 2p_x=π 2p_y)<σ 2p_z<(π^* 2p_x=π^* 2p_y)<σ^* 2p_z Key idea: For molecules with 14 or fewer electrons (... 1
- Resistance of a carbon resistor determined from colour codes is (22000±5\%) Ω. The colour of third band must be : Answer: 4. Orange Colour code: first two bands give the digits, the third band gives the power of ten (multiplier), the fourth gives toleran... 1
- The magnetic energy stored in an inductor of inductance 4 μH carrying a current of 2 A is : Answer: 1. 8 μ J Energy stored in an inductor: U=1/2LI² . U=1/2×(4×10⁻⁶)×(2)² = 8×10⁻⁶ J = 8 μ J. 1
- In a series LCR circuit, the inductance L is 10 mH, capacitance C is 1 μF and resistance R is 100 Ω. The frequency at which resonance occurs is : Answer: 1. 1.59 kHz Resonance occurs when X_L=X_C : f₀=1/2π√(LC) . Resistance does not affect it. LC=10×10⁻³×10⁻⁶=10⁻⁸ , so √(LC)=10⁻⁴ s. f₀... 1
- The magnitude and direction of the current in the following circuit is Answer: 3. 0.5 A from A to B through E In the loop the two cells oppose each other (10 V and 5 V), so the net emf is 10-5=5 V. The 10 V cell... 1
- The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of V volts is proportional to: Answer: 3. 1/V The shortest X-ray wavelength occurs when the electron gives all its kinetic energy to one photon: eV=dfrachcλ_min . λ_min=hc... 1
- The errors in the measurement which arise due to unpredictable fluctuations in temperature and voltage supply are : Answer: 1. Random errors Errors that arise from unpredictable, irregular fluctuations in conditions such as temperature or voltage supply ar... 1
- For Young's double slit experiment, two statements are given below:Statement I : If screen is moved away from the plane of slits, angular separation of the fringes remains constant.Statement II : If the monochromatic source is replaced by another mon… Answer: 4. Statement I is true but Statement II is false. Fringe width β=λ D/d , so angular separation θ=β/D=λ/d . Statement I: θ does not d... 1
- A bullet is fired from a gun at the speed of 280 m s^-1 in the direction 30^° above the horizontal. The maximum height attained by the bullet is (g=9.8 m s^-2,\ 30^°=0.5) : Answer: 4. 1000 m Maximum height: H=u²sin²θ/2g . H=(280)²(0.5)²/2×9.8=78400×0.25/19.6=1000 m. The answer is 1000 m. 1
- A Carnot engine has an efficiency of 50% when its source is at a temperature 327^° C. The temperature of the sink is : Answer: 2. 27^° C Carnot efficiency: η=1-T₂/T₁ with temperatures in kelvin. T₁=327+273=600 K, η=0.5⇒ T₂=0.5×600=300 K = 27^° C. The answer i... 1
- The amount of energy required to form a soap bubble of radius 2 cm from a soap solution is nearly : (surface tension of soap solution =0.03 N m^-1) Answer: 4. 3.01×10⁻⁴ J A soap bubble has two surfaces (inner and outer), so the energy needed equals surface tension times total area 2×4π r... 1
- The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to ≤ft(1/16)^th of its initial value? Answer: 1. 80 minutes Activity falls by half every half-life. dfrac116=(1/2)⁴ , so 4 half-lives are needed. t=4×20=80 minutes. The answer is... 1
- The potential energy of a long spring when stretched by 2 cm is U. If the spring is stretched by 8 cm, potential energy stored in it will be : Answer: 1. 16U Spring energy U=1/2kx²∝ x² . Extension goes from 2 cm to 8 cm, a factor of 4, so energy goes up by 4²=16 . The new energy is... 1
- The equivalent capacitance of the system shown in the following circuit is : Answer: 2. 2 μ F From the figure, one 3 μ F capacitor is in series with a parallel pair of 3 μ F capacitors. Parallel pair: 3+3=6 μ F. Serie... 1
- A vehicle travels half the distance with speed v and the remaining distance with speed 2v. Its average speed is: Answer: 4. 4v/3 Average speed = total distance / total time. Let the total distance be 2s . t₁=s/v , t₂=s/2v , total time =3s/2v . v_avg=2s/... 1
- The ratio of radius of gyration of a solid sphere of mass M and radius R about its own axis to the radius of gyration of the thin hollow sphere of same mass and radius about its axis is : Answer: Dropped in the official answer key: full marks to every candidate Radius of gyration is k=√(I/M) . Solid sphere about its axis: I=2/... 1
- Two bodies of mass m and 9m are placed at a distance R. The gravitational potential on the line joining the bodies where the gravitational field equals zero, will be (G = gravitational constant) : Answer: 4. -16Gm/R Find the point where the net field is zero, then add the potentials of both masses there. Let the point be at distance x... 1
- The venturi-meter works on : Answer: 3. Bernoulli's principle A venturi-meter measures the flow speed of a liquid in a pipe. In the narrow part the speed is higher and t... 1
- An ac source is connected to a capacitor C. Due to decrease in its operating frequency : Answer: 4. displacement current decreases. Capacitive reactance X_C=1/2π fC . When the frequency decreases, X_C increases. The current (and... 1
- The radius of inner most orbit of hydrogen atom is 5.3×10^-11 m. What is the radius of third allowed orbit of hydrogen atom? Answer: 1. 4.77 mathringA Bohr orbit radius: r_n=n² r₁ . Third orbit: r₃=9×5.3×10⁻¹¹=4.77×10⁻¹⁰ m = 4.77 Å (1 Å = 10⁻¹⁰ m). 1