Question 1
According to NCERT, which of the following vitamins can be stored in the body and does not need to be supplied regularly in diet?
✅ Correct Answer: Vitamin A
Explanation: Water-soluble vitamins (B group and C) must be supplied regularly in the diet because they are readily excreted in urine and cannot be stored in our body (except Vitamin B12). Fat-soluble vitamins (A, D, E, and K) are stored in the liver and adipose (fat-storing) tissues.
Question 2
A solution of ethanol and water containing approximately 95.4% ethanol by volume is an example of:
✅ Correct Answer: Minimum boiling azeotrope
Explanation: An ethanol-water mixture (95.4% ethanol) shows a large positive deviation from Raoult's law. Since the resulting vapor pressure is higher than expected, the solution boils at a lower temperature than either pure component, creating a minimum boiling azeotrope.
Question 3
Which of the following is the primary reason transition metals act as excellent catalysts, as specifically highlighted in NCERT?
✅ Correct Answer: Ability to adopt multiple oxidation states and form complexes
Explanation: Transition metals and their compounds are renowned for their catalytic activity. This property is ascribed directly to their ability to adopt multiple oxidation states and form unstable intermediate complexes, allowing them to provide alternative reaction pathways with much lower activation energy.
Question 4
Read the following statement from NCERT regarding the cleansing action of soaps. The hydrocarbon tail of the soap molecule is:
✅ Correct Answer: Hydrophobic and dissolves in the oil/grease droplet
Explanation: Soap molecules have a dual-nature structure. The long non-polar hydrocarbon tail is hydrophobic (water-repelling) and readily dissolves in the dirt/oil/grease. The polar head (carboxylate ion) is hydrophilic (water-loving) and remains interacting with the water, facilitating micelle formation.
Question 5
Among the following molecular species, which one has the highest bond order and is diamagnetic?
✅ Correct Answer: $N_2$
Explanation: Using Molecular Orbital Theory (MOT):
$O_2$ has Bond Order (BO) = 2, paramagnetic.
$O_2^+$ has BO = 2.5, paramagnetic.
$N_2$ has BO = 3 (14 electrons), and all electrons are paired up in the MO diagram, making it strictly diamagnetic.
$N_2^+$ has BO = 2.5, paramagnetic.
Question 6
Which of the following pairs of compounds are enantiomers?
✅ Correct Answer: D-Glucose and L-Glucose
Explanation: Enantiomers are non-superimposable mirror images of each other. The 'D' and 'L' configurations of Glucose are exact mirror images at every single chiral center. Glucose and Galactose/Mannose are epimers (diastereomers that differ at a single carbon), and Fructose is a structural isomer (a ketose vs an aldose).
Question 7
In electrophilic aromatic substitution, the presence of a $-NO_2$ group on the benzene ring:
✅ Correct Answer: Deactivates the ring and directs the electrophile to the meta position.
Explanation: The nitro group ($-NO_2$) shows incredibly strong $-I$ and $-R$ effects. It aggressively withdraws electron density from the benzene ring, strongly deactivating it. The electron density is reduced the most at the ortho and para positions due to resonance, making the meta position relatively more electron-rich for an incoming electrophilic attack.
Question 8
The boiling point of $o$-nitrophenol is significantly lower than that of $p$-nitrophenol. The correct conceptual reason is:
✅ Correct Answer: $o$-nitrophenol undergoes intramolecular hydrogen bonding, preventing association between molecules.
Explanation: In $o$-nitrophenol, the $-OH$ and $-NO_2$ groups are adjacent to each other on the ring, allowing for intramolecular (within the same molecule) hydrogen bonding. This structurally prevents the molecules from associating with each other. In contrast, $p$-nitrophenol forms strong intermolecular hydrogen bonds, leading to molecular association and a much higher boiling point.
Question 9
Assertion (A): The specific conductivity of an electrolytic solution decreases with a decrease in concentration.
Reason (R): The number of ions per unit volume that carry the current in a solution decreases on dilution.
✅ Correct Answer: Both (A) and (R) are true and (R) is the correct explanation of (A).
Explanation: Specific conductivity ($\kappa$) is defined as the conductance of exactly $1\text{ cm}^3$ of the solution. When an electrolytic solution is diluted, its total volume increases drastically. This means the number of current-carrying ions per unit volume strictly decreases, leading to a direct drop in specific conductivity.
Question 10
Assertion (A): $SF_6$ is kinetically inert and structurally highly stable, rendering it unreactive towards hydrolysis.
Reason (R): The six fluorine atoms form a tight steric shield around the central sulfur atom, preventing the attack of water molecules.
✅ Correct Answer: Both (A) and (R) are true and (R) is the correct explanation of (A).
Explanation: Even though the S-F bonds are highly polar, $SF_6$ remains highly unreactive. The central sulfur atom is octahedrally surrounded by six bulky and highly electronegative fluorine atoms. These atoms act as a dense steric shield, physically blocking nucleophiles like $H_2O$ from attacking the sulfur's vacant d-orbitals.
Question 11
Read the following statements regarding solid-state defects:
Statement I: Frenkel defect is a dislocation defect that does not change the overall density of the crystal.
Statement II: Schottky defect is a vacancy defect that leads to a decrease in the overall density of the crystal.
✅ Correct Answer: Both Statement I and Statement II are correct.
Explanation: The Frenkel defect occurs when a smaller ion (usually the cation) is dislocated from its normal site to an interstitial site; since no mass is lost, density remains constant. The Schottky defect involves an equal number of missing cations and anions leaving the crystal lattice; mass decreases while volume stays constant, heavily lowering the density.
Question 12
Given below are two statements regarding coordination compounds:
Statement I: $[Co(NH_3)_6]^{3+}$ is a diamagnetic inner orbital complex.
Statement II: $NH_3$ always acts as a weak field ligand regardless of the central metal ion's oxidation state.
✅ Correct Answer: Statement I is true, Statement II is false.
Explanation: Statement I is true. $Co^{3+}$ is a $3d^6$ system. In the presence of $NH_3$ (which acts as a strong field ligand with $Co^{3+}$), forced pairing occurs, leaving two 3d orbitals vacant for $d^2sp^3$ (inner orbital) hybridization. Statement II is false because $NH_3$ acts as a strong field ligand specifically with $Co^{3+}$ and $Cu^{2+}$, meaning its field strength isn't "always" weak.
Question 13
The time required for 99% completion of a first-order reaction is $x$ times the time required for its 90% completion. The value of $x$ is:
✅ Correct Answer: 2
Explanation: For a first-order reaction, $t = \frac{2.303}{k} \log \frac{a}{a-x}$.
For 99% completion: $t_{99} = \frac{2.303}{k} \log \frac{100}{100-99} = \frac{2.303}{k} \log 100 = \frac{2.303}{k} \times 2$.
For 90% completion: $t_{90} = \frac{2.303}{k} \log \frac{100}{100-90} = \frac{2.303}{k} \log 10 = \frac{2.303}{k} \times 1$.
Therefore, $t_{99} = 2 \times t_{90}$, so $x=2$.
Question 14
What is the standard free energy change ($\Delta G^\circ$) for a reaction if its equilibrium constant $K_c$ is 10 at $300\text{ K}$?
(Given $R \approx 8.314\text{ J K}^{-1}\text{mol}^{-1}$, $\ln 10=2.303$)
✅ Correct Answer: $-5.74\text{ kJ mol}^{-1}$
Explanation: Thermodynamics Formula: $\Delta G^\circ = -2.303 RT \log K_c$
$\Delta G^\circ = -2.303 \times 8.314 \times 300 \times \log 10$
$\Delta G^\circ = -2.303 \times 2494.2 \times 1$
$\Delta G^\circ \approx -5744\text{ J mol}^{-1} = -5.74\text{ kJ mol}^{-1}$.
Question 15
A $0.1\text{ M}$ aqueous solution of a weak monobasic acid is $1\%$ ionized at $298\text{ K}$. What is the dissociation constant ($K_a$) of the acid?
✅ Correct Answer: $1 \times 10^{-5}$
Explanation: Degree of dissociation ($\alpha$) = $1\% = 0.01$. Concentration ($C$) = $0.1\text{ M}$.
Using Ostwald's dilution law for weak acids ($\alpha \ll 1$): $K_a = C\alpha^2$.
$K_a = 0.1 \times (0.01)^2 = 0.1 \times 0.0001 = 1 \times 10^{-5}$.
Question 16
Which of the following reactions does NOT yield a primary amine as the major product?
✅ Correct Answer: Reaction of methyl isocyanide with $LiAlH_4$
Explanation: Methyl isocyanide ($CH_3-NC$) upon strong reduction yields a secondary amine ($CH_3-NH-CH_3$). In contrast, Gabriel phthalimide synthesis, Hoffmann bromamide degradation, and the reduction of nitrobenzene all specifically produce pure primary amines ($1^\circ$ amines).
Question 17
Consider the reaction:
$$CH_3-CH_2-CH(Br)-CH_3 \xrightarrow{\text{alc. KOH, } \Delta} \text{Major Product}$$
The major product formed is governed by:
✅ Correct Answer: Saytzeff's (Zaitsev) rule
Explanation: When 2-bromobutane is heated with alcoholic KOH, it undergoes intense dehydrohalogenation ($\beta$-elimination). According to Saytzeff's rule, the more highly substituted alkene (But-2-ene) is the major product because it is thermodynamically much more stable due to hyperconjugation.
Question 18
An optically active coordination complex of Cobalt has the formula $[Co(en)_2Cl_2]^+$. Which specific isomer of this complex shows optical isomerism?
✅ Correct Answer: The cis-isomer only
Explanation: In $[M(AA)_2a_2]$ type complexes, the trans-isomer possesses a plane of symmetry, making it achiral and completely optically inactive. The cis-isomer lacks any plane or center of symmetry, making it chiral, and therefore it exists as non-superimposable dextro and laevo optical isomers.
Question 19
For the gas-phase reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, how is the equilibrium constant $K_p$ mathematically related to $K_c$?
✅ Correct Answer: $K_p = K_c(RT)^{-2}$
Explanation: The relationship is given by $K_p = K_c(RT)^{\Delta n_g}$.
$\Delta n_g = (\text{moles of gaseous products}) - (\text{moles of gaseous reactants})$.
$\Delta n_g = 2 - (1 + 3) = 2 - 4 = -2$.
Therefore, substituting the value gives $K_p = K_c(RT)^{-2}$.
Question 20
What is the true oxidation state of Chromium ($Cr$) in Chromium pentoxide ($CrO_5$)?
✅ Correct Answer: +6
Explanation: If calculated using standard linear rules: $x + 5(-2) = 0 \implies x = +10$, which is physically impossible (Chromium has a max group oxidation state of +6). Structurally, $CrO_5$ has a "butterfly" structure containing two peroxide linkages ($O-O$, oxidation state -1 for 4 oxygen atoms) and one normal double bond with oxygen (oxidation state -2).
Accurate Calculation: $x + 4(-1) + 1(-2) = 0 \implies x = +6$.
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