#neet
- The correction factor 'a' to the ideal gas equation corresponds to Answer: 4. forces of attraction between the gas molecules In the van der Waals equation (P+an²/V²)(V-nb)=nRT , the term a corrects the press... 1
- Magnesium reacts with an element (X) to form an ionic compound. If the ground state electronic configuration of (X) is 1s^2 2s^2 2p^3, the simplest formula for this compound is Answer: 4. Mg ₃ X ₂ X has configuration 1s²2s²2p³ , so it is nitrogen and forms mathrmX³⁻ . Magnesium forms mathrmMg²⁺ . Balancing charges:... 1
- Iron exhibits bcc structure at room temperature. Above 900°C, it transforms to fcc structure. The ratio of density of iron at room temperature to that at 900°C (assuming molar mass and atomic radii of iron remains constant with temperature) is Answer: 2. 3√(3)/4√(2) Density =Z M/a³ N_A . Since M and atomic radius r are the same, compare Z/a³ . bcc: Z=2 , a=4r/sqrt3 . fcc: Z=4 , a=2... 1
- Consider the following species :CN^+, CN^-, NO and CNWhich one of these will have the highest bond order ? Answer: 3. CN ^- Count electrons and fill the molecular orbitals. CN^- : 14 electrons, bond order 3 (isoelectronic with N₂ , CO). CN: 13 ele... 1
- Which one is a wrong statement ? Answer: 2. The electronic configuration of N atom is1s ² 2s ² 2p _x¹ 2p _y¹ 2p _z¹ shown as orbital box diagram: 1s [up down], 2s [up down],... 1
- Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity ? Answer: 1. N ₂ O ₅ N₂O , NO and NO₂ are all released by natural processes (soil bacteria, lightning) and by human activity (fuel combustion,... 1
- Hydrocarbon (A) reacts with bromine by substitution to form an alkyl bromide which by Wurtz reaction is converted to gaseous hydrocarbon containing less than four carbon atoms. (A) is Answer: 4. CH ₄ The alkyl bromide undergoes Wurtz coupling, mathrm2R-Br+2Na→ R-R+2NaBr . The product has twice the carbon count of R, and mu... 1
- The compound A on treatment with Na gives B, and with PCl_5 gives C. B and C react together to give diethyl ether. A, B and C are in the order Answer: 4. C ₂ H ₅ OH, C ₂ H ₅ ONa, C ₂ H ₅ Cl A is ethanol. C₂H₅OH+Na→ C₂H₅ONa (B), and C₂H₅OH+PCl₅→ C₂H₅Cl (C). B and C then react by Will... 1
- The compound C_7H_8 undergoes the following reactions :C_7H_8 3\ Cl_2/Δ A Br_2/Fe B Zn/HCl CThe product 'C' is Answer: 1. m-bromotoluene Work through the sequence: C₇H₈ is toluene. 3 Cl₂/Δ : side-chain chlorination gives benzotrichloride, C₆H₅CCl₃ (A)... 1
- Identify the major products P, Q and R in the following sequence of reactions :benzene + CH_3CH_2CH_2Cl Anhydrous AlCl_3 P ; P [(ii) H_3O^+/Δ](i) O_2 Q + R Answer: 4. P = cumene (C ₆ H ₅ CH(CH ₃ ) ₂ ), Q = phenol (C ₆ H ₅ OH), R = CH ₃ - CO - CH ₃ Friedel-Crafts alkylation with n-propyl chloride... 1
- Which of the following compounds can form a zwitterion ? Answer: 4. Glycine A zwitterion needs both an acidic group and a basic group in the same molecule, so the proton moves from the acid to the... 1
- Which of the following statements is *correct* ? Answer: 1. Ovules are not enclosed by ovary wall in gymnosperms. Gymnosperms are 'naked-seeded' plants, so their ovules lie exposed and are... 1
- Which of the following oxides is most acidic in nature ? Answer: 3. BeO Acidic character of oxides falls as the metallic character of the element rises. In group 2, MgO, CaO and BaO are basic (basi... 1
- A block of mass m is placed on a smooth inclined wedge ABC of inclination θ as shown in the figure. The wedge is given an acceleration 'a' towards the right. The relation between a and θ for the block to remain stationary on the wedge is Answer: 4. a=gtanθ For the block to stay at rest on the smooth wedge accelerating right with a , in the wedge frame use a pseudo force ma on... 1
- A toy car with charge q moves on a frictionless horizontal plane surface under the influence of a uniform electric field E. Due to the force q E, its velocity increases from 0 to 6 m/s in one second duration. At that instant the direction of the fiel… Answer: 3. 1 m/s, 3 m/s Phase 1 (0 to 1 s): a=6\ m/s² , displacement =1/2·6·1=3 m, ending at 6 m/s. Phase 2 (1 to 3 s): the acceleration rev... 1
- A moving block having mass m, collides with another stationary block having mass 4m. The lighter block comes to rest after collision. When the initial velocity of the lighter block is v, then the value of coefficient of restitution (e) will be Answer: 3. 0.25 Momentum conservation: mv=0+4mv₂⇒ v₂=v/4 (lighter block at rest, v₁=0 ). Coefficient of restitution = relative speed of sepa... 1
- A body initially at rest and sliding along a frictionless track from a height h (as shown in the figure) just completes a vertical circle of diameter AB = D. The height h is equal to Answer: 4. 5/4 D To just complete the vertical circle of radius R=D/2 , the speed at the top B must satisfy v_B²=gR . Energy conservation fr... 1
- Three objects, A : (a solid sphere), B : (a thin circular disk) and C : (a circular ring), each have the same mass M and radius R. They all spin with the same angular speed ω about their own symmetry axes. The amounts of work (W) required to bring th… Answer: 1. W_C>W_B>W_A Work needed to stop each body equals its rotational kinetic energy, W=1/2Iω² . Same M , R , ω , so W∝ I . Solid spher... 1
- Which one of the following statements is incorrect ? Answer: 4. Coefficient of sliding friction has dimensions of length. Check each statement. Rolling friction is smaller than sliding friction... 1
- A solid sphere is in rolling motion. In rolling motion a body possesses translational kinetic energy (K_t) as well as rotational kinetic energy (K_r) simultaneously. The ratio K_t:(K_t+K_r) for the sphere is Answer: 3. 5 : 7 For a solid sphere rolling without slipping, K_t=1/2mv² and K_r=1/2Iω²=1/2·2/5mR²·v²/R²=1/5mv² . K_t/K_t+K_r=1/2/1/2+1/5=5/... 1
- A solid sphere is rotating freely about its symmetry axis in free space. The radius of the sphere is increased keeping its mass same. Which of the following physical quantities would remain constant for the sphere ? Answer: 4. Angular momentum The sphere is in free space, so there is no external torque and angular momentum L=Iω is conserved. When the rad... 1
- If the mass of the Sun were ten times smaller and the universal gravitational constant were ten times larger in magnitude, which of the following is not correct ? Answer: 4. 'g' on the Earth will not change. Check each statement with M_sun→ M/10 and G→10G . The Earth's g=GM_e/R_e² becomes 10 times larg... 1
- The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are K_A, K_B and K_C, respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then Answer: 3. K_A>K_B>K_C By conservation of angular momentum (Kepler's second law), a planet moves faster when it is closer to the Sun, so its... 1
- Given van der Waals constant for NH_3, H_2, O_2 and CO_2 are respectively 4.17, 0.244, 1.36 and 3.59, which one of the following gases is most easily liquefied ? Answer: 1. NH ₃ The more easily a gas liquefies, the stronger its intermolecular attraction, and the van der Waals constant a measures exact... 1