IGNOU BCHCT-131 June 2025 Previous Year Question Paper

Q1.Write your enrolment number, course code and part clearly on the two answer sheets.

(iii) Marks are indicated against each question. Part—A (Marks : 25) Note : Attempt any five questions.

Q2.(a) State postulates of Bohr’s atomic theory. 4

(b) Write the equation for Einstein’s theory of photoelectric effect.

Q3.(a) Calculate the de-Broglie wavelength associated with an electron having mass

Q4.109x10*!kg moving with a velocity of 2.190x10° ms. 2

(b) State three applications of Schrédinger equation.

Q5.(a) Explain why Oj is paramagnetic and o> is diamagnetic. 3

(b) Write Lewis structures of SF, and CO, molecules.

Q6.(a) Arrange the following isoelectric ions in increasing order of ionic radii. Also give reason of your answer : 3 02-,F-, Na*,Mg2*, Al?*

(b) Explain why the electron affinity values of halogens are large and negative.

Q7.(a) State and explain Pauli’s exclusion principle. 1

(b) Write the electronic configuration of Cr and explain. (Atomic No. Cr = 24). 2

(c) Write the hybridisation of each carbon atom in the following : 2 CH; -C =C-CHg,

Q8.(a) State the four quantum numbers that are assigned to an electron and write their significance. 4

(b) Using VSEPR theory, predict the shape of NHs.

Q9.(a) Write two main contributing resonance structures of NH3. 2

(b) State Heisenberg’s uncertainty principle. 1

(c) Draw the molecular orbitals formed by the combination of s-p, atomic orbitals. Also name these orbitals. 2 Part—B (Marks : 25) Note : Attempt any five questions.

Q10.(a) Which of the following compounds can exhibit geometrical isomerism ? 2

(i) C)H;C = CC,H;

(ii) Cj,H;CH =CHC,H; Write the structure of Z isomer of that compound.

(b) Define the following : 3 @) Plane polarised light Gi) Dextrorotation Gii) Resolution

Q11.(a) Which of the following cycloalkanes has least angle strain ? Why ? 3

(iii)

(b) Define octane number. Write the IUPAC name of alkane which has been assigned : 2

(i) highest octane number

(1) highest cetane number

Q12.(a) Which alkene on ozonolysis will give acetone and ethyl methyl ketone ? Write the reaction and give IUPAC name of the alkene. 3

(b) Explain why aniline is a weaker base than benzylamine.

Q13.(a) Identify the following compounds as aromatic/not aromatic. Give reasons in eae [J 3 “oT

(b) Why is meso-tartaric acid optically inactive ? Explain.

Q14.(a) Assign the configuration as R or S to the following compounds after giving the priorities of the groups : 3 CH; i we C @ yp | Os Gi) H” i> CH3 OCH;

(b) Write the products of the following reactions : 2 @) Hydration of propyne

(ii) Reduction of propyne with H, in presence of Pd-C (BaSO,) .

Q15.(a) Arrange the following acids in an increasing order of acidity and explain your answer : 3 (ij) CH,CH,COOH

(ii) CH,C1CH,COOH

(iii) CH; CH- COOH

(b) What are homolytic and _heterolytic reactions ? Give one example of each.

Q16.(a) Write stepwise mechanism of the following reaction : 3 CH,CH,CH,X —SO#@")_, CH3CH = CH,

(b) Draw the chair and boat conformations of cyclohexane. Which of these is less stable and why ? 2 OF, Na*,Mg?*, Al?* CH, -C =C-CH, @) CH,C=CC,H,

(ii) C,H,;CH =CHC,H; ii) fatter

(iii) oo)

(iii) C) @ uw” pret GH) go" pron (ij) CH,CH,COOH

(ii) CH,C1CH,COOH

(ii) CH, CH- COOH CH,CH,CH,x =e KOH _, CH,CH = CH,