NEET UG
- Which of the following biphenyls is optically active ? Answer: 2. [structure shown in figure] Key idea: a biphenyl is optically active (shows atropisomerism) only if rotation about the central bo... 1
- The pair of electron in the given carbanion, CH_3C C^, is present in which of the following orbitals ? Answer: 4. sp Key idea: the carbanion carbon in CH₃Cequiv C^- is triply bonded to another carbon, so it has 2 regions of electron density an... 1
- Which of the following features is not present in the Phylum - Arthropoda ? Answer: 3. Parapodia Key idea: Arthropods have a chitinous exoskeleton, a metamerically segmented body and jointed appendages. Parapodia are... 1
- Name the chronic respiratory disorder caused mainly by cigarette smoking : Answer: 1. Emphysema Key idea: Cigarette smoking mainly causes emphysema. Smoke damages the alveolar walls, so the surface area for gas exch... 1
- In context of Amniocentesis, which of the following statement is incorrect ? Answer: 4. It can be used for detection of Cleft palate. Key idea: Amniocentesis tests fluid-borne foetal cells for chromosomal and metaboli... 1
- Two electrons occupying the same orbital are distinguished by : Answer: 4. Spin quantum number Key idea: two electrons in the same orbital have the same n, l and m. By the Pauli exclusion principle they m... 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
- Match the compounds given in column I with the hybridisation and shape given in column II and mark the correct option.Column I: (a) XeF_6; (b) XeO_3; (c) XeOF_4; (d) XeF_4Column II: (i) distorted octahedral; (ii) square planar; (iii) pyramidal; (iv)… Answer: 1. (i) (iii) (iv) (ii) Key idea: use VSEPR for each xenon compound. XeF₆ : sp³d³ , 6 bond pairs + 1 lone pair, distorted octahedral... 1
- Predict the correct order among the following : Answer: 1. lone pair - lone pair > lone pair - bond pair > bond pair - bond pair Key idea (VSEPR): a lone pair is held only by one nucleus,... 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
- Consider the following liquid - vapour equilibrium.Liquid ⇌ VapourWhich of the following relations is correct ? Answer: 4. dln P/dT = Δ H_v/RT² Key idea: this is the Clausius-Clapeyron equation for liquid-vapour equilibrium: dln P/dT=Δ H_v/RT² Vapour p... 1
- The correct thermodynamic conditions for the spontaneous reaction at all temperatures is : Answer: 3. Δ H < 0 and Δ S > 0 Key idea: Δ G=Δ H-TΔ S . A reaction is spontaneous at all temperatures when Δ G<0 for every T. This needs Δ H... 1
- 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
- Which one of the following statements is correct when SO_2 is passed through acidified K_2Cr_2O_7 solution ? Answer: 4. Green Cr₂(SO₄)₃ is formed. Key idea: SO₂ is a reducing agent and acidified dichromate is an oxidising agent. mathrmCr₂O₇²⁻+3SO₂+2... 1
- The electronic configurations of Eu (Atomic No. 63), Gd (Atomic No. 64) and Tb (Atomic No. 65) are : Answer: 4. [Xe]4f⁷6s² , [Xe]4f⁷5d¹6s² and [Xe]4f⁹6s² Key idea: half-filled 4f⁷ is extra stable, and Gd and Tb follow from it. Eu (63): [Xe]4... 1
- Match items of Column I with the items of Column II and assign the correct code :Column I: (a) Cyanide process; (b) Froth floatation process; (c) Electrolytic reduction; (d) Zone refiningColumn II: (i) Ultrapure Ge; (ii) Dressing of ZnS; (iii) Extrac… Answer: 1. (iv) (ii) (iii) (i) Key idea: match each process with its use. (a) Cyanide process: extraction of gold (Au), iv. (b) Froth floata... 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
- Consider the nitration of benzene using mixed conc. H_2SO_4 and HNO_3. If a large amount of KHSO_4 is added to the mixture, the rate of nitration will be : Answer: 2. slower Key idea: nitration needs the nitronium ion, formed by HNO₃+2H₂SO₄⇌ NO₂^++H₃O^++2HSO₄^- KHSO₄ adds a large amount of HSO₄^... 1
- Which of the following reagents would distinguish cis-cyclopenta-1, 2-diol from the trans-isomer ? Answer: 1. Acetone Key idea: only the cis-1,2-diol has both -OH groups on the same side of the ring, so it can form a cyclic five-membered k... 1
- The product formed by the reaction of an aldehyde with a primary amine is : Answer: 1. Schiff base Key idea: an aldehyde (or ketone) condenses with a primary amine with loss of water to give an imine, R-CH=N-R' , als... 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 copper is heated with conc. HNO_3 it produces : Answer: 1. Cu(NO₃)₂ and NO₂ Key idea: the reduction product of nitric acid depends on its concentration. Cu+4HNO₃(conc.)→ Cu(NO₃)₂+2NO₂+2H₂O... 1
- The product obtained as a result of a reaction of nitrogen with CaC_2 is : Answer: 1. Ca(CN)₂ Key idea: calcium carbide absorbs nitrogen at high temperature to give calcium cyanamide (nitrolim) and carbon. CaC₂+N₂→... 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