#neet
- The correct structure of 2,6-Dimethyl-dec-4-ene is : Answer: 1. [skeletal structure - see figure] Key idea: build the chain from the name: 10 carbons (dec), a double bond between C-4 and C-5, a... 1
- A ball of mass 0.15 kg is dropped from a height 10 m, strikes the ground and rebounds to the same height. The magnitude of impulse imparted to the ball is (g = 10 m/s^2) nearly : Answer: 2. 4.2 kg m/s Key idea: impulse equals change in momentum; the velocity reverses. Speed at the ground v=√(2gh)=√(200)≈14.1 m/s. Rebo... 1
- A step down transformer connected to an ac mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit ? Answer: 1. 0.2 A Key idea: with no losses, input power = output power = 44 W. I_p=P/V_p=44/220=0.2 A. Option 1. (The secondary current is 44... 1
- A particle moving in a circle of radius R with a uniform speed takes a time T to complete one revolution.If this particle were projected with the same speed at an angle 'θ' to the horizontal, the maximum height attained by it equals 4R. The angle of… Answer: 4. θ = sin⁻¹(2gT²/π²R)^(1/2) Key idea: speed v=dfrac2π RT , and the maximum height is H=v²sin²θ/2g . 4R=4π²R²/T²·sin²θ/2g⇒sin²θ=8gRT... 1
- A particle of mass 'm' is projected with a velocity v = kV_e (k < 1) from the surface of the earth. (V_e = escape velocity)The maximum height above the surface reached by the particle is : Answer: 4. Rk²/1-k² Key idea: conserve energy: 1/2mv²-dfracGMmR=-GMm/R+h , with V_e²=dfrac2GMR . 1/2m k²dfrac2GMR-dfracGMmR=-GMm/R+h⇒dfracGM... 1
- Three resistors having resistances r_1, r_2 and r_3 are connected as shown in the given circuit. The ratio i_3/i_1 of currents in terms of resistances used in the circuit is : Answer: 2. r₂/r₂+r₃ Key idea: r₂ and r₃ are in parallel, and the current i₁ splits in inverse ratio of resistances (current divider). i₃=i₁·... 1
- From a circular ring of mass 'M' and radius 'R' an arc corresponding to a 90° sector is removed. The moment of inertia of the remaining part of the ring about an axis passing through the centre of the ring and perpendicular to the plane of the ring i… Answer: 1. 3/4 Key idea: moment of inertia of a ring about its axis depends only on mass and radius, since every part is at distance R. Remo... 1
- Which one among the following is the correct option for right relationship between C_P and C_V for one mole of ideal gas ? Answer: 2. C_P - C_V = R Key idea: for one mole of an ideal gas, C_P exceeds C_V by exactly R (Mayer's relation). At constant pressure, heat... 1
- The correct option for the number of body centred unit cells in all 14 types of Bravais lattice unit cells is : Answer: 4. 3 Key idea: count the body-centred (I) cells among the 14 Bravais lattices. Cubic: primitive, body-centred, face-centred (1 body-... 1
- Noble gases are named because of their inertness towards reactivity. Identify an incorrect statement about them. Answer: 2. Noble gases have very high melting and boiling points. Key idea: noble gases are monoatomic and held only by very weak dispersion... 1
- The major product formed in dehydrohalogenation reaction of 2-Bromo pentane is Pent-2-ene. This product formation is based on ? Answer: 1. Saytzeff's Rule Key idea: in dehydrohalogenation, the more substituted (more stable) alkene is the major product. This is Saytzef... 1
- The compound which shows metamerism is : Answer: 4. C₄H₁₀O Key idea: metamerism occurs between compounds with the same functional group (usually ethers, ketones, secondary amines) b... 1
- BF_3 is planar and electron deficient compound. Hybridization and number of electrons around the central atom, respectively are : Answer: 3. sp² and 6 Key idea: BF₃ has three bond pairs and no lone pair on boron. Three electron domains give sp² hybridisation and trigona... 1
- The right option for the statement "Tyndall effect is exhibited by", is : Answer: 3. Starch solution Key idea: the Tyndall effect needs colloidal particles large enough (1 to 1000 nm) to scatter light. Starch forms... 1
- Among the following alkaline earth metal halides, one which is covalent and soluble in organic solvents is : Answer: 4. Beryllium chloride Key idea: small, highly polarising mathrmBe²⁺ gives strong covalent character (Fajans' rules). BeCl₂ is covale... 1
- Which one of the following methods can be used to obtain highly pure metal which is liquid at room temperature ? Answer: 3. Distillation Key idea: the metal liquid at room temperature is mercury, which is volatile with a low boiling point (630 K). Disti... 1
- For a reaction A→B, enthalpy of reaction is -4.2 kJ mol^-1 and enthalpy of activation is 9.6 kJ mol^-1. The correct potential energy profile for the reaction is shown in option. Answer: 2. [graph option - see figure] Key idea: Δ H<0 means the product B lies below reactant A; activation enthalpy 9.6 kJ/mol means the p... 1
- Which one of the following polymers is prepared by addition polymerisation ? Answer: 1. Teflon Key idea: addition polymers form from unsaturated monomers by chain addition; condensation polymers lose small molecules.... 1
- The major product of the following chemical reaction is :(CH_3)_2CH-CH=CH_2 + HBr (C_6H_5CO)_2O_2 ? Answer: 1. (CH₃)₂CH-CH₂-CH₂-Br Key idea: with peroxide, HBr adds to alkenes by a free-radical path: anti-Markovnikov (Kharasch peroxide effe... 1
- Choose the correct option for graphical representation of Boyle's law, which shows a graph of pressure vs. volume of a gas at different temperatures : Answer: 4. [graph option - see figure] Key idea: Boyle's law: PV=constant at fixed T, so P vs V is a rectangular hyperbola. A higher T gives... 1
- A radioactive nucleus ^A_ZX undergoes spontaneous decay in the sequence^A_ZX → _Z-1B → _Z-3C → _Z-2D, where Z is the atomic number of element X. The possible decay particles in the sequence are : Answer: 3. β^+, α, β^- Key idea: α decay lowers Z by 2; β^- raises Z by 1; β^+ lowers Z by 1. Z→ Z-1 : β^+ . Z-1→ Z-3 : α . Z-3→ Z-2 : β^- .... 1
- An inductor of inductance L, a capacitor of capacitance C and a resistor of resistance 'R' are connected in series to an ac source of potential difference 'V' volts as shown in figure.Potential difference across L, C and R is 40 V, 10 V and 40 V, res… Answer: 4. 5\ Ω Key idea: voltages in series LCR add as phasors: V=√(V_R²+(V_L-V_C)²) , and Z=V/I with both in the same (rms) form. V=√(40²+... 1
- The escape velocity from the Earth's surface is v. The escape velocity from the surface of another planet having a radius, four times that of Earth and same mass density is : Answer: 4. 4v Key idea: v_e=√(2GM/R) and M=4/3π R³ρ , so v_e∝ Rsqrtρ . Same density and radius four times as large gives v_e'=4v . Option 4. 1
- A screw gauge gives the following readings when used to measure the diameter of a wireMain scale reading : 0 mmCircular scale reading : 52 divisionsGiven that 1 mm on main scale corresponds to 100 divisions on the circular scale. The diameter of the… Answer: 4. 0.052 cm Key idea: diameter = main scale reading + circular reading × least count. Least count =1\ mm/100=0.01 mm. Diameter =0+52... 1