#neet
- Identify the major product obtained in the following reaction :2-acetylbenzaldehyde (benzene ring with ortho -COCH_3 and -CHO) + 2[Ag(NH_3)_2]^+ + 3 ^-OH Δ major product Answer: 4. ring with -COCH ₃ and -COO ^- (structure) Key idea: Tollens' reagent [Ag(NH₃)₂]^+ in base is a mild oxidant: it oxidises aldehyde... 1
- Identify the final product [D] obtained in the following sequence of reactions.CH_3CHO [ii)\ H_3O^+]i)\ LiAlH_4 [A] [Δ]H_2SO_4 [B] HBr [C], then [C] + bromobenzene Na/dry\ ether [D] Answer: 2. ethylbenzene (structure) Key idea: Follow the sequence, ending with a Wurtz-Fittig reaction. CH₃CHO with LiAlH₄ gives ethanol [A]... 1
- A very long conducting wire is bent in a semi-circular shape from A to B as shown in figure. The magnetic field at point P for steady current configuration is given by : Answer: 4. μ₀ i/4R[1-2/π] pointed away from page Add the fields of the three parts at P: two semi-infinite straight wires and one semicircle... 1
- In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin)? Answer: 4. -100 cm Add the powers of the two refracting surfaces of the lens ( n=1.5 ) placed in a medium of index 1.6 , using P=n₂-n₁/R . S... 1
- Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be : Answer: 1. Infinite For lenses in contact, 1/F=dfrac1f₁+dfrac1f₂ . f₁=+f , f₂=-f : 1/F=1/f-1/f=0 , so F=∞ . The combination behaves like a p... 1
- A wire carrying a current I along the positive x-axis has length L. It is kept in a magnetic field B=(2i+3j-4k) T. The magnitude of the magnetic force acting on the wire is : Answer: 4. 5 IL Force on a wire: vec F=I vec L×vec B with vec L=Lhat i . hat i×(2hat i+3hat j-4hat k)=3hat k+4hat j (since hat i×hat j=hat k... 1
- A bullet from a gun is fired on a rectangular wooden block with velocity u. When bullet travels 24 cm through the block along its length horizontally, velocity of bullet becomes u/3. Then it further penetrates into the block in the same direction bef… Answer: 2. 27 cm Assume a constant resistive force, so deceleration a is constant. Use v²=u²-2as . First 24 cm: (u/3)²=u²-2a(24)⇒ 48a=8u²/9⇒... 1
- An electric dipole is placed as shown in the figure. The electric potential (in 10^2 V) at point P due to the dipole is (ε_0 = permittivity of free space and 1/4πε_0=K): Answer: 2. (3/8)qK P lies on the axis of the dipole. Distances from P: to +q it is 5-3=2 cm, to -q it is 5+3=8 cm. V=Kq(dfrac10.02-dfrac10.0... 1
- A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity 4 m s^-1. The ball strikes the water surface after 4 s. The height of bridge above water surface is (Take g=10 m s^-2… Answer: 4. 64 m Take upward as positive. The ball starts with u=+4 m/s, and its displacement at the water is -h after 4 s. s=ut-1/2gt²⇒ -h=4... 1
- Taking stability as the factor, which one of the following represents correct relationship? Answer: 1. TlI > TlI ₃ Key idea: In group 13 the +1 state becomes more stable down the group because of the inert pair effect; for Tl, +1 is... 1
- Identify the product in the following reaction :Benzenediazonium chloride (C_6H_5N_2^+Cl^-) with (i) Cu_2Br_2/HBr (ii) Mg/dry ether (iii) H_2O → Product Answer: 3. benzene (structure) Key idea: Follow each step: Sandmeyer reaction, then Grignard formation, then hydrolysis. C₆H₅N₂^+Cl^- with C... 1
- The given compoundC_6H_5-CH=CH-CH(X)-CH_2CH_3 (benzene ring attached to CH=CH-CH(X)-CH_2CH_3)is an example of ________. Answer: 4. allylic halide Key idea: A halide is named by the carbon that carries the halogen. In C₆H₅-CH=CH-CH(X)-CH₂CH₃ , X is on an sp³ ca... 1
- In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with Fe^3+ due to the formation of - Answer: 1. [Fe(SCN)]²⁺ Key idea: When N and S are both present, Na fusion forms sodium thiocyanate, NaSCN, in the Lassaigne's extract. Na +... 1
- Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :Assertion A : A reaction can have zero activation energy.Reasons R : The minimum extra amount of energy absorbed by reactant molecules so that thei… Answer: 1. A is false but R is true. Key idea: Activation energy is the extra energy reactants must absorb to reach the threshold energy: E_... 1
- The right option for the mass of CO_2 produced by heating 20 g of 20% pure limestone is (Atomic mass of Ca = 40)CaCO_3 1200\ K CaO + CO_2 Answer: 3. 1.76 g Key idea: Only the pure CaCO₃ decomposes; find its moles and use 1:1 mole ratio with CO₂ . Pure CaCO₃ = 20 × 20/100 = 4 g.... 1
- Complete the following reaction :cyclohexanone [A] HCN cyclohexanone cyanohydrin (1-hydroxycyclohexanecarbonitrile) [B] [Δ]conc.\ H_2SO_4 [C][C] is ________. Answer: 1. cyclohex-1-ene-1-carboxylic acid (structure) Key idea: Conc. H₂SO₄ with heat does two things to a cyanohydrin: it hydrolyses -CN... 1
- Given below are two statements :Statement I : A unit formed by the attachment of a base to 1' position of sugar is known as nucleosideStatement II : When nucleoside is linked to phosphorous acid at 5'-position of sugar moiety, we get nucleotide.In th… Answer: 4. Statement I is true but Statement II is false. Key idea: Nucleoside = base + sugar; nucleotide = nucleoside + phosphoric acid. St... 1
- A compound is formed by two elements A and B. The element B forms cubic close packed structure and atoms of A occupy 1/3 of tetrahedral voids. If the formula of the compound is A_xB_y, then the value of x + y is in option Answer: 2. 5 Key idea: In ccp, if B atoms number N, there are N octahedral and 2N tetrahedral voids. Take 1 unit cell: B = 4 atoms; tetrahed... 1
- The stability of Cu^2+ is more than Cu^+ salts in aqueous solution due to - Answer: 4. hydration energy. Key idea: Stability in aqueous solution depends on the overall enthalpy change, where hydration enthalpy often... 1
- Match List - I with List - II :List - I: A. Coke B. Diamond C. Fullerene D. GraphiteList - II: I. Carbon atoms are sp^3 hybridised. II. Used as a dry lubricant III. Used as a reducing agent IV. Cage like moleculesChoose the correct answer from the op… Answer: 4. A-III, B-I, C-IV, D-II Key idea: Match each form of carbon with its structure or use. A. Coke is used as a reducing agent in meta... 1
- Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :Assertion A : Helium is used to dilute oxygen in diving apparatus.Reasons R : Helium has high solubility in O_2.In the light of the above statement… Answer: 4. A is true but R is false. Key idea: Gases dissolve in blood at high pressure; helium is chosen because it is hardly soluble. Asse... 1
- Some tranquilizers are listed below. Which one from the following belongs to barbiturates? Answer: 1. Veronal Key idea: Barbiturates are derivatives of barbituric acid. Veronal (barbital) is a barbiturate (others: luminal, seconal)... 1
- Which of the following statements are NOT correct?A. Hydrogen is used to reduce heavy metal oxides to metals.B. Heavy water is used to study reaction mechanism.C. Hydrogen is used to make saturated fats from oils.D. The H-H bond dissociation enthalpy… Answer: 4. D, E only Key idea: Check each statement. A. True: H₂ reduces oxides of less active (heavy) metals. B. True: D₂O is used as a tra... 1
- For a certain reaction, the rate = k[A]^2[B], when the initial concentration of A is tripled keeping concentration of B constant, the initial rate would Answer: 4. increase by a factor of nine. Key idea: Rate is proportional to [A]² when B is constant. New rate = k(3[A])²[B] = 9k[A]²[B] , so... 1