Join Online Classes for October Exam 2025
Complete Course, Revision, PYQs, Sample Papers
Call and WhatsAppNIOS April 2025 Sr. Secondary Chemistry (313) Solved Paper
SECTION: A
MCQ Questions
Question number 1 to 16 are multiple choice questions of 1 mark each.
1. Tertiary amines have:
a) One lone pair of electrons on nitrogen
b) Two lone pairs of electrons
c) No lone pair on nitrogen
d) Three hydrogen atoms on nitrogen
View Answer
One lone pair of electrons on nitrogen.
2. Which of the following is most acidic?
a) Butanoic acid
b) 2-chlorobutanoic acid
c) 3-chlorobutanoic acid
d) 4-chlorobutanoic acid
View Answer
2-chlorobutanoic acid.
3. The hybridization of oxygen in ethers is:
a) sp
b) sp2
c) sp3
d) dsp2
View Answer
sp3
4. Butan-1-ol on reaction with PCC gives:
a) Butanone
b) Propanal
c) Butanal
d) Butanoic acid
View Answer
Butanal.
5. The organometallic compounds obtained by the reaction of magnesium metal with alkyl or aryl halides are called:
a) Grignard reagents
b) Bayer’s reagents
c) Fehling’s solution
d) Hinsberg’s reagent
View Answer
Grignard reagents.
6. Alkenes and alkynes can be distinguished by:
a) Br2/CCl4
b) Alkaline KMnO4
c) Ammoniacal AgNO3
d) H2/Pd
View Answer
Alkaline KMnO4.
7. Enantiomers are:
a) Superimposable mirror images of a compound
b) Non-superimposable mirror images of a compound
c) Superimposable compounds
d) Non-superimposable compounds
View Answer
Non-superimposable mirror images of a compound.
8. The empirical formula of S3O9 is:
a) SO2
b) SO3
c) S2O4
d) S4O12
View Answer
SO3.
9. Which of the following is not necessary for the molar volume of a gas?
a) 0°C
b) 1 bar
c) 1 mole
d) 278 K
View Answer
278 K.
10. The number of moles present in 73.0 g of HCl is:
a) 1
b) 2
c) 3
d) 4
View Answer
2.
11. Law of definite proportions states that:
a) A given compound always contains exactly the same proportion of elements by mass
b) The same elements can combine in different ratios to form different compounds
c) The composition can vary
d) Atoms can be variable
View Answer
A given compound always contains exactly the same proportion of elements by mass.
12. The mass number of an atom is the sum of:
a) Electrons and protons
b) Electrons and neutrons
c) Neutrons and protons
d) Protons only
View Answer
Neutrons and protons.
13. The formation of ionic compound is favored by:
a) High ionization energy of metal
b) Low ionization energy of metal
c) Low electron affinity of non-metal
d) Low lattice energy
View Answer
Low ionization energy of metal.
14. The isotope of hydrogen with two neutrons is:
a) Protium
b) Deuterium
c) Tritium
d) Both B and C
View Answer
Tritium.
15. The correct order of acid strength of oxoacids of chlorine is:
a) HOClO3 > HOClO2 > HOClO > HOCl
b) HOCl > HOClO2 > HOClO > HOClO3
c) HOCl > HOClO > HOClO2 > HOClO3
d) HOClO3 > HOClO > HOClO2 > HOCl
View Answer
HOClO3 > HOClO2 > HOClO > HOCl.
16. Two elements with almost identical atomic radii due to lanthanoid contraction are:
a) La and Lu
b) Ce and Lu
c) Zr and Hf
d) Ce and Hf
View Answer
Zr and Hf.
Read also NIOS Sr. Secondary Chemistry April 2024 MCQs with Answer
NIOS Sr. Secondary Chemistry April 2023 MCQs with Answer
NIOS Sr. Secondary Chemistry October 2022 MCQs with Answer
NIOS Sr. Secondary Chemistry October 2021 MCQs with Answer
NIOS Sr. Secondary Chemistry MCQs with Answer
Question number 17 to 28 are objective type questions of 2 mark each.
17. Write True (T) for correct statement and False (F) for incorrect statement:
(1) In Buna-S, Bu stands for butadiene, Na for sodium and S for styrene.
Answer: True (T)
(2) Chloroprene is a polymer obtained from neoprene.
Answer: False (F)
18. Read the passage given below and answer the following questions.
Detergents are widely used as cleaning agents. When dissolved in water, its molecules tend to concentrate at the surface of the solution or at interface. Their hydrophilic group makes them soluble in water. Depends on the nature of hydrophilic part synthetic detergents are anionic, cationic or non-ionic type.
(1) Name the anion present in detergents.
Answer: Sulphate ion (SO₄²⁻) or sulphonate ion depending on detergent type
(2) How many carbon atoms in sodium lauryl sulphate carbon chain?
Answer: 12 carbon atoms
19. Write True (T) for correct statement and False (F) for incorrect statement:
(1) Hybrid orbitals of a molecule are all unequivalent orbitals and have different energies.
Answer: False (F)
(2) On the basis of VSEPR, methane molecule is tetrahedral.
Answer: True (T)
20. Read the passage given below and answer the following questions.
Alcohols have hydroxyl group as a functional group. When the hydroxyl group is attached to primary, secondary and tertiary carbon atom, the alcohols are known as primary, secondary and tertiary alcohols. They hardly exhibit any acidic character. They are generally toxic in nature. On dehydration they either produce alkenes or ethers.
(1) Name a test to distinguish primary, secondary, and tertiary alcohols.
Answer: Lucas test
(2) Conditions to produce ether from ethanol?
Answer: Concentrated sulfuric acid, 140°C temperature
21. Match Column I with Column II:
(a) [PtCl6]2- → (2) oxidation state 4
(b) [Ag(NH3)2]+ → (1) oxidation state 1
(c) [Fe(CN)6]4- → (3) oxidation state 2
(d) [Cr(H2O)4Cl2]+ → (4) oxidation state 3
22. Complete the following by given options below
2, 3, diamagnetic, paramagnetic, ferromagnetic
(1) Bond order of nitrogen molecule is 3
(2) Molecules with all paired electrons are diamagnetic.
23. Complete the following by given options below
acidic, basic, amphoteric, carnalite, chile salt peter
(1) Hydroxide of aluminium is amphoteric
(2) Common ore of magnesium is carnallite
24. Read the passage given below and answer the following questions.
Sulphuric acid is known as the king of chemicals. It is used in the manufacture of fertilizers, paints and pigments, detergents etc. Dilute sulphuric acid is obtained from concentrated sulphuric acid. Improper method of dilution throws out drops of sulphuric acid and may cause burns.
(1) Which property of sulphuric acid converts carbohydrates into black carbon mass?
Answer: Dehydrating property
(2) How is concentrated sulphuric acid diluted?
Answer: By slowly adding acid to water with stirring.
25. Complete reactions:
(1) CH2=CH2 + H2O → CH3CH2OH (with H2SO4 and heat)
(2) CH3CHBr2 + alc. KOH → CH2=CHBr + KBr + H2O (elimination reaction).
26. Read the passage given below and answer the following questions.
The elements from groups 3 to 12 occupy the middle portion of the periodic table. The last electron is filled in the penultimate d-subshell. These elements are metallic in nature. The d-block elements represent a change from the most electropositive s-block to the least electropositive p-block and hence are called transition elements.
The following questions are multiple choice questions.
Choose the most apropriate answer
Identify the correct statement among the following
(a) Zn, Cd, and Hg are not considered transition elements
(b) d orbitals can hold a maximum of 5 electrons
(c) Transition elements shows low melting amd boiling points.
(d) Densities of transition elements are low as compared to than those of s-block elements
Answer: (a) Zn, Cd, and Hg are not considered transition elements because their d-orbitals are completely filled in the ground as well as common oxidation states.
(2) Why is copper regarded as a transition element despite its 3d¹⁰4s¹ configuration?
Answer: Because copper can have an incomplete d-orbital in its excited state and forms cations with incomplete d-subshells, qualifying it as a transition element.
27. Complete the following by given options below
distance, mass, velocity, weak, strong
(1) The principal quantum number determines the ----- of the electron from the nucleus.
Answer: distance
(2) The electrostatic force of attraction between the ions in an ionic compound is -----.
Answer: strong
28. Read the passage given below and answer the following questions.
Water is an inorganic, miracle compound. It exist in three forms- solid, liquid and vapour. In winters, lakes freeze and forms ice on the surface on water.
(1) "H2O and HF, though covalent compounds, have high boiling points." Justify.
Answer: Due to strong hydrogen bonding between molecules.
(2) Why is solid water (ice) less dense than liquid water?
Answer: Because ice has an open hexagonal structure formed by hydrogen bonding, making it less dense than liquid water.
SECTION: B
Question number 29 to 43 are subjective type questions. An internal choice has been provided in some of these questions.
29. A sample of lime juice has a hydronium ion concentration of 7.3×10−2 M. Calculate its pH.
[log 7.3 = 0.8633, log 10 = 1].
Answer: pH = −log[H3O+]
log[H3O+] = log7.3 + log10−2
= 0.8633 + (−2) = 0.8633 − 2 = −1.1367
Therefore, pH = −log [H3O+] = − (− 1.1367 ) = 1.1367
pH = −log[H3O+] = −(−1.1367) = 1.1367
Calculate the pH of a solution containing 0.05 M benzoic acid and 0.025 M sodium benzoate. Benzoic acid has a pH of 4.2.
[log 2 = 0.3010]
Answer: Use the Henderson-Hasselbalch equation:
pH = pKa + log [Base]/[Acid]
pH = 4.2 + log(0.025/0.05)
pH = 4.2 + log 0.05
pH = 4.2 + log 1/2
pH = 4.2 + -log2
pH = 4.2 −0.3010
pH = 3.899
30. Define a closed system. Give an example.
Answer: A closed system is defined as a system that can exchange energy (such as heat or work) with its surroundings but does not allow the exchange of matter across its boundaries.
Example: A good example of a closed system is a thermos flask containing a hot beverage. The thermos can transfer heat energy to or from its surroundings (though ideally very little), but the liquid inside does not leave or enter the flask, so matter is not exchanged.
31. Define enthalpy of formation. The enthalpy of formation of CO2(g) is 393.5 kJ mol−1. Represent this in the form of a chemical equation.
Answer: The enthalpy of formation (denoted as ΔHf) is the enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states under standard conditions (usually 1 atm pressure and 25°C or 298 K).
It measures the energy absorbed or released during the formation of a compound from its elemental forms.
C(s,graphite) + O2(g) → CO2(g) ΔHf = −393.5 kJ/mol
The bond dissociation energies for the first and second steps of H2O dissociation are 502 kJ mol−1 and 427 kJ mol−1 respectively. Represent them in chemical equations.
Answer: The dissociation of water occurs in two steps with the given bond dissociation energies:
1st Step: Breaking the O-H bond to form hydroxyl radical and hydrogen atom.
H2O → OH* + H* ΔH = 502 kJ mol−1
2nd Step: Breaking the second O-H bond (from hydroxyl radical) to form oxygen atom and hydrogen atom.
OH* → O* + H* ΔH = 427 kJ mol−1
These chemical equations represent the sequential bond dissociation steps in water with their corresponding bond dissociation energies (BDEs).
32. Draw a graph for a liquid pair A and B, depicting negative deviation from Raoult's law.
ORDefine Van't Hoff factor. What will be its value when the solute undergoes dissociation in solution?
Answer: The Van't Hoff factor (i) is defined as the ratio of the total number of particles (ions or molecules) in solution after the solute dissolves and dissociates/associates, to the number of formula units initially dissolved.
When a solute dissociates into ions in solution, the Van't Hoff factor (i) is greater than 1.
33. Define Bronsted-Lowry concept of acids and bases. Identify Bronsted-Lowry acid and base in the reaction:
NH3 + HF → NH4+ + F−
Answer: A Bronsted-Lowry acid is a substance that donates a proton (H⁺ ion) to another substance.
A Bronsted-Lowry base is a substance that accepts a proton (H⁺ ion) from another substance.
NH3 + HF → NH4+ + F−
HF acts as the Bronsted-Lowry acid because it donates a proton (H⁺) to NH3.
NH3 acts as the Bronsted-Lowry base because it accepts a proton (H⁺) from HF.
34. What is a buffer solution? Give one example each of acidic and basic buffer.
Answer: A buffer solution is a solution that resists significant change in pH when small amounts of an acid or base are added. It maintains the pH relatively constant by neutralizing added hydrogen ions (H⁺) or hydroxide ions (OH⁻).
Buffer solutions usually contain:
A weak acid and its conjugate base, or
A weak base and its conjugate acid.
Examples:
Acidic buffer: A mixture of acetic acid (CH3COOH) and its salt sodium acetate (CH3COONa)
This buffer maintains a pH less than 7.
Basic buffer: A mixture of ammonium hydroxide (NH4OH) and its salt ammonium chloride (NH4Cl)
This buffer maintains a pH greater than 7.
35. What is the essence of Hess's law of constant heat summation? What is a useful application of this law?
Hess's law states that the total enthalpy change in a chemical reaction is the same whether the reaction occurs in one step or multiple steps.
This law is a direct consequence of the first law of thermodynamics (conservation of energy) and allows calculation of enthalpy changes for reactions that are difficult to measure directly by breaking them into simpler steps whose enthalpy changes are known.
Hess's law is widely applied to:
a. Calculate the enthalpy change (ΔH) for reactions that cannot be carried out directly or are too slow.
b. Determine heats of formation of compounds.
c. Find lattice energies of ionic compounds.
d. Calculate heats of combustion or transition.
e. Analyze reaction mechanisms by summing intermediate steps' enthalpy changes.
Are ∆Hsub∘ and ∆Hfusion∘ the same or different? Justify.
Answer: These two are different processes and therefore have different values. Furthermore, according to Hess's law, the enthalpy of sublimation is equal to the sum of the enthalpy of fusion and the enthalpy of vaporization (∆Hsub∘ and ∆Hfusion∘):
ΔHsub∘ = ∆Hfusion∘ + ∆Hvap∘
This is because sublimation involves two steps: first melting (fusion), then vaporization.
36. Why do transition metals show catalytic properties? Explain.
Answer: Transition metals exhibit catalytic properties because of the following reasons:
a. Variable Oxidation States: Transition metals can exist in multiple oxidation states by gaining or losing electrons from their partially filled d-orbitals. This ability enables them to participate in oxidation-reduction reactions easily, facilitating electron transfer that lowers activation energy for reactions.
b. Presence of Vacant or Partially Filled d-Orbitals: These d-orbitals allow transition metals to form intermediate complexes with reactant molecules through coordinate bonding. This bonding weakens reactant bonds, making it easier for the reaction to proceed.
c. Ability to Adsorb Reactants on Their Surface: Finely divided transition metals have a large surface area with free valence orbitals where reactant molecules get adsorbed. This increases the local concentration of reactants, aligns molecules suitably, and weakens bonds – effectively lowering the activation energy.
d. Formation of Intermediate Compounds: Transition metals can form unstable intermediate compounds during reaction pathways that provide an alternative route with lower activation energy.
37. What happens when benzene reacts with chlorine in the presence of iron as a catalyst? Give the chemical equation and name the type of reaction.
Answer: When benzene reacts with chlorine in the presence of iron as a catalyst, an electrophilic aromatic substitution reaction occurs. The hydrogen atom on the benzene ring is replaced by a chlorine atom, forming chlorobenzene and hydrogen chloride.
2Fe+3 + Cl2 → 2FeCl3
C6H6 + Cl2 → C6H5Cl + HCl
Type of reaction: Electrophilic aromatic substitution
38. The vapour pressure of water is 12.3 kPa at 300 K. Calculate the vapour pressure of 1 molal solution of a solute in it.
Answer: To calculate the vapor pressure of a 1 molal solution of a solute in water where the vapor pressure of pure water is 12.3 kPa at 300 K, use Raoult's Law:
Psolution = Xsolvent × P∘solvent
Moles of water = 1000 g/18 g/mol ≈ 55.56 mol
Total moles = moles of solute + moles of solvent = 1 + 55.56 = 56.56
Xsolvent = 55.56/56.56 ≈ 0.9823
Psolution = 0.9823 × 12.3 = 12.08 kPa