Question

Read the passage given below and answer the following questions: The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since d electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group. In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage. A. Assertion and reason both are correct statements and reason is correct explanation for assertion. B. Assertion and reason both are correct statements but reason is not correct explanation for assertion. C. Assertion is correct statement but reason is wrong statement. D. Assertion is wrong statement but reason is correct statement. 1) Assertion: Cations of transition elements occur in various valence states Reason: Large number of oxides of transition elements are possible. 2) Assertion: Crystal structure of oxides of transition metals often show defects. Reason: Ligand field effect cause distortions in crystal structures. 3) Assertion : Transition metals form protective oxide films. Reason: Oxides of transition metals are always stoichiometric. 4) Assertion: CrO crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by chromium ions. Reason: Transition metal oxide may be hexagonal close-packed lattice of oxide ions with metal ions filling the octahedral voids.

Molecular Nitrogen \(N_2\) comprises about 78% by volume of Earth’s atmosphere. It occurs as Sodium nitrate, \(NaNO_3\)(chile saltpeter) & Potassium nitrate, \(KNO_3\)(Indian altpeter) in earth’s crust. Since nitrate are very soluble in water so these are not wide spread in the earth’s crust. Nitrogen is also an important constituent of amino acids, protein & nucleic acids in plants & animals. Nitrogen shows anomalous behavior from rest of the elements due to following reasons; Smaller size, high ionization enthalpy, high electronegativity & absence of d-orbital. It has unique ability to form p∏-p∏ multiple bonds with itself & with small size atoms like C & O as they have small size & high electronegativity. Heavier elements of this group do not form p∏-p∏ bonds as their atomic orbitals are so large & diffuse that they can’t have effective overlapping. Thus Nitrogen exists as diatomic molecules \(N_2\) with a triple bond. Consequently, its bond enthalpy (941.4 KJ \(mol^{-1}\)) is very high. P, As & Sb form only single bonds as P-P, As-As & Sb-Sb. Due to much bond enthalpy N is much less reactive than P. Single N-N bond is weaker than single P-P bond due to high interelectronic repulsion of the non bonding electrons, owing to small bond length. As a result, the catenation tendency is weaker in nitrogen. Hence nitrogen exists as gas while phosphorus exists as solid. Nitrogen can’t form d∏- d∏ bond due to absence of d- orbitals so it can’t expand its covalency beyond four as heavier members can. The following questions are multiple choice questions. choose the most appropriate answer. 1) Among group 15 elements which exists as gas at room temperature a) Arsenic b) Bismuth c) Nitrogen d) Phosphorous 2) The stability of +5 oxidation state decreases and that of +3 state increases down the group in group 15 elements due to a) inert pair effect b) decrease in ionisation enthalpy c) increase in size d) shielding effect 3) Nitrogen is restricted to a maximum covalency of 4 because of a) absence of d-orbitals b) presence of d-orbitals c) absence of s and p-orbitals d) none of the above 4) Extra pure \(N_2\) can be obtained by heating a) \(NH_3\) with CuO b) \(NH_4NO_3\) c) \(\left(NH_4\right)_2Cr_2O_7\) d) \(Ba\left(N_3\right)_2\) 5) Catenation tendency is weaker in nitrogen, because of a) single N–N bond is weaker b) single N–N bond is stronger c) ability to form pi bonds by N atoms d) none of the above

Read the passage given below and answer the following questions: When a protein in its native form, is subjected to physical changes like change in temperature or chemical changes like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein. The denaturation causes change in secondary ann tertiary structures but primary structures remain intact. Examples of denaturation of protein are coagulation of egg white on boiling, curdling of milk, formation of cheese when an acid is added to milk. Choose the most appropriate answer: i) Mark the wrong statement about denaturation of proteins. a) The primary structure of the protein does not change. b) Globular proteins are converted into fibrous proteins. c) Fibrous proteins are converted into globular proteins. d) The biological activity of the protein is destroyed. ii) Which structure{s) of proteins remains(s) intact during denaturation process? (a) Both secondary and tertiary structures (b) Primary structure only (c) Secondary structure only (d) Tertiary structure only iii) a-helix a n d β - pleated structures of proteins are classified as (a) primary structure (b) secondary structure (c) tertiary structure (d) quaternary structure. (iv) Secondary structure of protein refers to a) mainly denatured proteins and structure of prosthetic groups. b) three-dimensional structure, especially the bend between. amino acid residues that are distant from each other in the polypeptide chain. c) linear sequence of amino acid residues in the polypeptide chain. d) regular folding patterns of continuous portions of the polypeptide chain.

Read the passage given below and answer the following questions: In an ideal crystal, there must be regular repeating arrangement of the constituting particles and its entropy must be zero at absolute zero temperature. However, it is impossible to obtain an ideal crystal and it suffers from certain defects called imperfections. In pure crystal, these defects arises either due to disorder or dislocation of the constituting particles from the normal positions or due to the movement of the particles even at absolute zero temperature. Such defects increase with rise in temperature. In addition to these certain defects arise due to the presence of some impurities. Such defects not only modify the existing properties of the crystalline solids but also impart certain new characteristics to them. Answer the following MCQs by choosing the most appropriate options: 1) AgCl is crystallized from molten AgCl containing a little \(CdCl_2\). The solid obtained will have (a) cationic vacancies equal to number of \(Cd^{2+}\) ions incorporated. (b) cationic vacancies equal to double the number of \(Cd^{2+}\) ions. (c) anionic vacancies. (d) neither cationic nor anionic vacancies. 2) Lattice defect per \(10^{15}\) NaCl is 1. What is the number of lattice defects in a mole of NaCl? (a) 6.02 × \(10^{23}\) (b) 6.02 × \(10^8\) (c) \(10^{14}\) (d) None of these 3) The ionic substances in which the cation and anion are of almost similar size shows (a) non-stoichiometric defect (b) Schottky defect (c) Frenkel defect (d) all of these 4) Which of the following gives both Frenkel and Schottky defect? (a) AgCl (b) CsCl (c) KCl (d) AgBr

The sequence of bases along the DNA and RNA chain establishes its primary structure which controls the specific properties of the nucleic acid. An RNA molecule is usually a single chain of ribose-containing nucleotide. On the basis of X-ray analysis of DNA, J.D., Watson and F.H.C. CYST (shared noble prize in 1962) proposed a three dimensional secondary structure for DNA. DNA molecule is a long and highly complex, spirally twisted, double helix, ladder like structure. The two polynucleotide chains or strands are linked up by hydrogen bonding between the nitrogenous base molecules of their nucleotide monomers. Adenine (purine) always links with thymine (pyrimidine) with the help of two hydrogen bonds and guanine (purine) with cytosine (pyrimidine) with the help of three hydrogen bonds. Hence, the two strands extend in opposite directions, i.e., are antiparallel and complimentary. In these questions (Q. No. i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. a) Assertion and reason both are correct statements and reason is correct explanation for assertion. b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. c) Assertion is correct statement but reason is wrong statement d) Assertion is wrong statement but reason is correct statement. i) Assertion - DNA molecules and RNA molecules are found in the nucleus of a cell. Reason : There are two types of nitrogenous bases, purines and pyrimidines. Adenine (A) and guanine (G)are substituted purines; cytokine (C), thymine (T) arid uracil (U) are substituted pyrimidines. ii) Assertion .- In both DNA and RNA, heterocyclic base and phosphate ester linkages are at C- 1’ and C-5’respectively of the sugar molecule. Reason : Nucleotides and nucleosides mainly differ from each other in presence of phosphate units. iii)Assertion .- The backbone of RNA molecule is a linear chain consisting of an alternating units of heterocylic base, D-ribose and a phosphate. Reason : The segment of RNA which acts as the instruction manual for the synthesis of protein is ribose. iv) Assertion.- In DNA, the complementary bases are, adenine and guanine; thymine and cytosine. Reason : The phenomenon of mutation is chemical change in DNA molecule.

The solubility of gases increases with increase of pressure. William Henry made a systematic investigation of the solubility of a gas in a liquid. According to Henry’s law “the mass of a gas dissolved per unit volume of the solvent at constant temperature is directly proportional to the pressure of the gas in equilibrium with the solution”. Dalton during the same period also concluded independently that the solubility of a gas in a liquid solution depends upon the partial pressure of the gas. If we use the mole fraction of gas in the solution as a measure of its solubility, then Henry’s law can be modified as “the partial pressure of the gas in the vapour phase is directly proportional to the mole fraction of the gas in the solution”. Answer the following MCQs by choosing the most appropriate options: (i) Henry’s law constant for the solubility of methane in benzene at 298 K is 4.27 × \(10^5\) mm Hg. The solubility of methane in benzene at 298 K under 760 mm Hg is (a) 4.27 × \(10^{-5}\) (b) 1.78 × \(10^{-3}\) (c) 4.27 × \(10^{-3}\) (d) 1.78 × \(10^{-3}\) (ii) The partial pressure of ethane over a saturated solution containing 6.56 × \(10^{-2}\) g of ethane is 1 bar. If the solution contains 5.00 × \(10^{-2}\) g of ethane then what will be the partial pressure (in bar) of the gas? (a) 0.762 (b) 1.312 (c) 3.81 (d) 5.0 (iii) KH (K bar) values for Ar(g), \(CO_2\)(g), HCHO(g) and \(CH_4\)(g) are 40.39, 1.67, 1.83 × \(10^{-5}\) and 0.413 respectively. Arrange these gases in the order of their increasing solubility. (a) HCHO < \(CH_4\) < \(CO_2\) < Ar (b) HCHO < \(CO_2\) < \(CH_4\) < Ar (c) Ar < \(CO_2\) < \(CH_4\) < HCHO (d) Ar < \(CH_4\) < \(CO_2\) < HCHO (iv) When a gas is bubbled through water at 298 K, a very dilute solution of the gas is obtained. Henry’s law constant for the gas at 298 K is 150 K bar. If the gas exerts a partial pressure of 2 bar, the number of millimoles of the gas dissolved in 1 L of water is (a) 0.55 (b) 0.87 (c) 0.37 (d) 0.66

Boiling point or freezing point of liquid solution would be affected by the dissolved solids in the liquid phase. A soluble solid in solution has the effect of raising its boiling point and depressing its freezing point. The addition of non-volatile substances to a solvent decreases the vapor pressure and the added solute particles affect the formation of pure solvent crystals. According to many researches the decrease in freezing point directly correlated to the concentration of solutes dissolved in the solvent. This phenomenon is expressed as freezing point depression and it is useful for several applications such as freeze concentration of liquid food and to find the molar mass of an unknown solute in the solution. Freeze concentration is a high quality liquid food concentration method where water is removed by forming ice crystals. This is done by cooling the liquid food below the freezing point of the solution. The freezing point depression is referred as a colligative property and it is proportional to the molar concentration of the solution (m), along with vapor pressure lowering, boiling point elevation, and osmotic pressure. These are physical characteristics of solutions that depend only on the identity of the solvent and the concentration of the solute. The characters are not depending on the solute’s identity. Answer the following MCQs by choosing the most appropriate options: (i) When a non volatile solid is added to pure water it will- (a) boil above \(100^\circ\)C and freeze above \(0^\circ\)C. (b) b) boil below \(100^\circ\)C and freeze above \(0^\circ\)C. (c) boil above \(100^\circ\)C and freeze below \(0^\circ\)C. (d) boil below \(100^\circ\)C and freeze below \(0^\circ\)C. (ii) Colligative properties are (a) dependent only on the concentration of the solute and independent of the solvent’s and solute’s identity. (b) dependent only on the identity of the solute and the concentration of the solute and independent of the solvent’s identity. (c) dependent on the identity of the solvent and solute and thus on the concentration of the solute. (d) dependent only on the identity of the solvent and the concentration of the solute and independent of the solute’s identity. (iii) Assume three samples of juices A, B and C have glucose as the only sugar present in them. The concentration of sample A, B and C are 0.1 M, 0.5 M and 0.2 M respectively. Freezing point will be highest for the fruit juice (a) A (b) B (c) C (d) all have same freezing point (iv) Identify which of the following is a colligative property? (a) Freezing point (b) Boiling point (c) Osmotic pressure (d) All of the above