MEC | Chemistry
The maximum number of electrons in the shell with $n = 3$ is
Answer: 18
Model set 1, Q53: explanation →The number of unpaired electrons in $\mathrm{Mn^{2+}}$ (Z = 25) is
Answer: 5
Model set 1, Q54: explanation →Which set of quantum numbers $(n, l, m)$ is NOT possible?
Answer: (2, 2, 1)
Model set 1, Q55: explanation →Which alkali metal salt imparts a golden yellow colour to the Bunsen flame?
Answer: sodium
Model set 1, Q70: explanation →The chemical formula of plaster of Paris is
Answer: $\mathrm{CaSO_4\cdot\tfrac{1}{2}H_2O}$
Model set 1, Q71: explanation →Froth flotation is used to concentrate
Answer: sulphide ores
Model set 1, Q72: explanation →The catalyst used in the contact process for sulphuric acid manufacture is
Answer: $\mathrm{V_2O_5}$
Model set 1, Q73: explanation →Copper reacts with dilute nitric acid to evolve mainly
Answer: NO
Model set 1, Q74: explanation →The halogen which exists as a liquid at room temperature is
Answer: bromine
Model set 1, Q75: explanation →The IUPAC name of $\mathrm{CH_3CH(CH_3)CH_2CH_3}$ is
Answer: 2-methylbutane
Model set 1, Q78: explanation →The number of structural isomers of $\mathrm{C_4H_{10}}$ is
Answer: 2
Model set 1, Q79: explanation →Which of the following shows optical isomerism?
Answer: butan-2-ol
Model set 1, Q93: explanation →The number of molecules in 11 g of carbon dioxide is (Avogadro number $N_A = 6.02\times10^{23}$)
Answer: $1.5\times10^{23}$
Model set 1, Q51: explanation →The mass of NaOH required to prepare 500 mL of 0.1 M solution is (Na = 23, O = 16, H = 1)
Answer: 2 g
Model set 1, Q52: explanation →The shape of the $\mathrm{NH_3}$ molecule is
Answer: trigonal pyramidal
Model set 1, Q56: explanation →The hybridisation of sulphur in $\mathrm{SF_6}$ is
Answer: $sp^3d^2$
Model set 1, Q57: explanation →A gas occupies 2 L at 1 atm. At constant temperature it is compressed to 0.5 L. The new pressure is
Answer: 4 atm
Model set 1, Q58: explanation →The ratio of the rates of diffusion of $\mathrm{H_2}$ and $\mathrm{O_2}$ under the same conditions is
Answer: 4 : 1
Model set 1, Q59: explanation →The pH of 0.01 M HCl solution is
Answer: 2
Model set 1, Q61: explanation →Which of the following pairs forms an acidic buffer?
Answer: $\mathrm{CH_3COOH + CH_3COONa}$
Model set 1, Q62: explanation →The mass of copper deposited when 2 A flows for 965 s through a $\mathrm{Cu^{2+}}$ solution is (Cu = 63.5, 1 F = 96500 C)
Answer: 0.635 g
Model set 1, Q64: explanation →$E^\circ$ of $\mathrm{Zn^{2+}/Zn}$ is $-0.76$ V and of $\mathrm{Cu^{2+}/Cu}$ is $+0.34$ V. The standard emf of the Zn-Cu cell is
Answer: 1.10 V
Model set 1, Q65: explanation →A first order reaction has $k = 0.0693\ \mathrm{min^{-1}}$. Its half-life is
Answer: 10 min
Model set 1, Q66: explanation →For a reaction with rate $= k[A]^2$, doubling the concentration of A makes the rate
Answer: four times
Model set 1, Q67: explanation →The most electronegative element is
Answer: fluorine
Model set 1, Q68: explanation →Which of the following has the highest first ionisation energy?
Answer: Ne
Model set 1, Q69: explanation →Ethene reacts with bromine in carbon tetrachloride to give
Answer: 1,2-dibromoethane
Model set 1, Q80: explanation →Propene reacts with HBr (Markovnikov addition) to give mainly
Answer: 2-bromopropane
Model set 1, Q81: explanation →Which of the following is the strongest acid?
Answer: $\mathrm{HCOOH}$
Model set 1, Q88: explanation →Ethanoic acid reacts with ethanol in the presence of conc. sulphuric acid to form
Answer: ethyl ethanoate
Model set 1, Q94: explanation →The suitable indicator for the titration of a strong acid with a weak base is
Answer: methyl orange
Model set 1, Q98: explanation →20 mL of 0.1 M NaOH neutralises 10 mL of a HCl solution. The molarity of the HCl is
Answer: 0.2 M
Model set 1, Q99: explanation →For $\mathrm{N_2 + 3H_2 \rightleftharpoons 2NH_3}$, increasing the pressure at constant temperature shifts the equilibrium
Answer: towards the product side
Model set 1, Q60: explanation →Given $\mathrm{C + O_2 \to CO_2}$, $\Delta H = -393$ kJ and $\mathrm{CO + \tfrac{1}{2}O_2 \to CO_2}$, $\Delta H = -283$ kJ, the $\Delta H$ for $\mathrm{C + \tfrac{1}{2}O_2 \to CO}$ is
Answer: -110 kJ
Model set 1, Q63: explanation →Which of the following ions is colourless in aqueous solution?
Answer: $\mathrm{Zn^{2+}}$
Model set 1, Q76: explanation →The oxidation state of chromium in $\mathrm{K_2Cr_2O_7}$ is
Answer: +6
Model set 1, Q77: explanation →Benzene is nitrated using
Answer: conc. $\mathrm{HNO_3}$ + conc. $\mathrm{H_2SO_4}$
Model set 1, Q82: explanation →Ethyl chloride on heating with aqueous KOH gives
Answer: ethanol
Model set 1, Q83: explanation →Which alcohol gives turbidity immediately with Lucas reagent at room temperature?
Answer: 2-methylpropan-2-ol
Model set 1, Q84: explanation →Phenol gives which colour with neutral ferric chloride solution?
Answer: violet
Model set 1, Q85: explanation →Diethyl ether is prepared by heating excess ethanol with conc. sulphuric acid at about
Answer: $140^\circ$C
Model set 1, Q86: explanation →Which compound gives a positive Tollens' test?
Answer: ethanal
Model set 1, Q87: explanation →Which of the following is the strongest base in aqueous solution?
Answer: dimethylamine
Model set 1, Q89: explanation →Gypsum is added to cement clinker during grinding in order to
Answer: slow down the setting
Model set 1, Q95: explanation →Soap is chemically the
Answer: sodium salt of a long-chain fatty acid
Model set 1, Q96: explanation →The percentage of nitrogen in urea, $\mathrm{CO(NH_2)_2}$, is about (N = 14, C = 12, O = 16, H = 1)
Answer: 46.7%
Model set 1, Q97: explanation →Which of the following is a non-reducing sugar?
Answer: sucrose
Model set 1, Q90: explanation →The linkage that joins amino acids in a protein is
Answer: $\mathrm{-CO-NH-}$
Model set 1, Q91: explanation →Nylon-6,6 is formed by the condensation of
Answer: hexamethylenediamine and adipic acid
Model set 1, Q92: explanation →Calcium salts impart which colour to a flame?
Answer: brick red
Model set 1, Q100: explanation →