Some Basic Concepts

18 JEE Main questions · Chemistry

ChemistryJEE Main 21 Jan 2026, Shift 1·Q6·MCQ·Moderate
Open
Eudiometry of hydrocarbon combustion
80 mL of a hydrocarbon on mixing with 264 mL of oxygen in a closed U-tube undergoes complete combustion. The residual gases after cooling to 273 K occupy 224 mL. When the system is treated with KOH solution, the volume decreases to 64 mL. The formula of the hydrocarbon is :
1. (1) $\ce{C2H4}$
2. (2) $\ce{C4H10}$
3. (3) $\ce{C2H2}$
4. (4) $\ce{C2H6}$
ChemistryJEE Main 21 Jan 2026, Shift 1·Q7·MCQ·Easy–moderate
Open
Stoichiometry and limiting reagent
14.0 g of calcium metal is allowed to react with excess HCl at 1.0 atm pressure and 273 K.
Which of the following statements is incorrect ?
[Given : Molar mass in g mol $^{-1}$ of Ca–40, Cl–35.5, H–1]
1. (1)0.35 mol of $\ce{H2}$ gas is evolved.
2. (2)7.84 L of $\ce{H2}$ gas is evolved.
3. (3)33.3 g of $\ce{CaCl2}$ is produced.
4. (4)The limiting reagent is calcium metal.
We corrected a printing error in the original paper
Source printed “33.3 of $\ce{CaCl2}$ is produced” (unit missing).
ChemistryJEE Main 21 Jan 2026, Shift 2·Q4·MCQ·Easy
Open
Stoichiometry of chlorine preparation
Aqueous HCl reacts with $\ce{MnO2(s)}$ to form $\ce{MnCl2(aq)}$ , $\ce{Cl2(g)}$ and $\ce{H2O}$ ( $l$ ). What is the weight (in g) of $\ce{Cl2}$ liberated when 8.7 g of $\ce{MnO2(s)}$ is reacted with excess aqueous HCl solution ? (Given Molar mass in g mol $^{-1}$ Mn $= 55$ , Cl $= 35.5$ , O $= 16$ , H $= 1$ )
1. (1)7.1
2. (2)71
3. (3)21.3
4. (4)14.2
ChemistryJEE Main 22 Jan 2026, Shift 1·Q6·MCQ·Easy–moderate
Open
Reaction stoichiometry gas volumes
In the reaction,
$\ce{2Al(s) + 6HCl(aq) -> 2Al^{3+}(aq) + 6Cl^{-}(aq) + 3H2(g)}$
which of the following statements is correct ?
1. (1)11.2 L $\ce{H2(g)}$ at STP is produced for every mole of HCl consumed.
2. (2)67.2 L $\ce{H2(g)}$ at STP is produced for every mole of Al that reacts.
3. (3)12 L HCl(aq) is consumed for every 6L $\ce{H2(g)}$ produced.
4. (4)33.6 L $\ce{H2(g)}$ is produced regardless of temperature and pressure for every mole of Al that reacts.
We corrected a printing error in the original paper
The source prints no question after the equation; “which of the following statements is correct ?” added.
ChemistryJEE Main 22 Jan 2026, Shift 2·Q1·MCQ·Easy–moderate
Open
Mole fraction of mixed solutions
At T(K), 100 g of 98% $\ce{H2SO4}$ (w/w) aqueous solution is mixed with 100 g of 49% $\ce{H2SO4}$ (w/w) aqueous solution. What is the mole fraction of $\ce{H2SO4}$ in the resultant solution ?
(Given : Atomic mass H = 1 u ; S = 32 u; O = 16 u)
(Assume that temperature after mixing remains constant)
1. (1)0.9
2. (2)0.1
3. (3)0.337
4. (4)0.663
We corrected a printing error in the original paper
Answer corrected; the source key is (4) — 0.663 is the mole fraction of water; $\ce{H2SO4}$ = 147/98 = 1.5 mol, water = 53/18 = 2.94 mol, so x( $\ce{H2SO4}$ ) = 0.337.
ChemistryJEE Main 22 Jan 2026, Shift 2·Q3·MCQ·Easy–moderate
Open
Stoichiometry and limiting reagent
$\ce{A + 2B -> AB2}$
36.0 g of ‘A' (Molar mass : 60 g mol $^{-1}$ ) and 56.0 g of ‘B' (Molar mass : 80 g mol $^{-1}$ ) are allowed to react. Which of the following statements are correct ?
- (A)‘A' is the limiting reagent
- (B)77.0 g of $\ce{AB2}$ is formed
- (C)Molar mass of $\ce{AB2}$ is 140 g mol $^{-1}$
- (D)15.0 g of A is left unreacted after the completion of reaction.
Choose the correct answer from the options given below :
1. (1)C and D only
2. (2)A and C only
3. (3)B and D only
4. (4)A and B only
We corrected a printing error in the original paper
Source printed “limting reagent” in statement A.
ChemistryJEE Main 23 Jan 2026, Shift 1·Q23·Numerical·Easy–moderate
Open
Acid base titration stoichiometry
x mg of pure HCl was used to make an aqueous solution. 25.0 mL of 0.1 M $\ce{Ba(OH)2}$ solution is used when the HCl solution was titrated against it. The numerical value of x is $\times\,10^{-1}$ . (Nearest integer)
Given : Molar mass of HCl and $\ce{Ba(OH)2}$ are 36.5 and 171.0 g mol $^{-1}$ respectively.
ChemistryJEE Main 24 Jan 2026, Shift 2·Q9·MCQ·Easy–moderate
Open
Percentage yield
A student has planned to prepare acetanilide from aniline using acetic anhydride. The student has started from 9.3 g of aniline. However, the student has managed to obtain 11 g of dry acetanilide.
The % yield of this reaction is :-
1. (1)81.5%
2. (2)97.5%
3. (3)59.5%
4. (4)72.5%
ChemistryJEE Main 28 Jan 2026, Shift 2·Q18·MCQ·Moderate
Open
Limiting reagent with mass percent solution
For the given reaction;
$\ce{CaCO3 + 2HCl -> CaCl2 + H2O + CO2}$
If 90 g $\ce{CaCO3}$ is added to 300 mL of HCl which contains 38.55% HCl by mass and has density 1.13 g mL $^{-1}$ , then which of the following option is correct?
Given molar mass of H, Cl, Ca and O are 1, 35.5, 40 and 16 g mol $^{-1}$ respectively.
1. (1)64.97 g of HCl remains unreacted
2. (2)32.85 g of $\ce{CaCO3}$ remains unreacted
3. (3)97.30 g of HCl reacted
4. (4)60.32 g of HCl remains unreacted
We corrected a printing error in the original paper
Source printed “CaCO $_3$ + 2HC1” (digit 1 for l) and, in option (4), “reamains”.
ChemistryJEE Main 2 Apr 2026, Shift 1·Q1·MCQ·Easy–moderate
Open
Stoichiometry of iron with steam
The mass of iron converted into $\ce{Fe3O4}$ by the action of 18 g of steam is :
(Given : Molar mass of H, O and Fe are 1, 16 and 56 g mol $^{-1}$ respectively)
Assume iron is present in excess :
1. (1)2.1 g
2. (2)4.2 g
3. (3)21 g
4. (4)42 g
ChemistryJEE Main 2 Apr 2026, Shift 2·Q1·MCQ·Easy–moderate
Open
Combustion stoichiometry of hydrocarbon
The ratio of mass percentage (w/w) of C : H in a hydrocarbon is 12 : 1. It has two carbon atoms. The weight (in g) of $\ce{CO2}$ (g) formed when 3.38 g of this hydrocarbon is completely burnt in oxygen is :
(Given : Molar mass in g mol $^{-1}$ C : 12, H : 1, O : 16)
1. (1)5.68
2. (2)11.44
3. (3)22.74
4. (4)17.05
ChemistryJEE Main 4 Apr 2026, Shift 1·Q1·MCQ·Easy
Open
Mole concept molar volume
Number of moles and number of molecules in 1.4187 L of $\ce{SO2}$ at STP respectively are
1. (1)0.1266; $3.812\times10^{22}$
2. (2)0.0633; $3.812\times10^{22}$
3. (3)0.1266; $7.6238\times10^{22}$
4. (4)0.0633; $7.6238\times10^{22}$
ChemistryJEE Main 4 Apr 2026, Shift 2·Q1·MCQ·Easy–moderate
Open
Mole concept number of atoms
The correct order of total number of atoms present in
- (A)2 moles of cyclohexane
- (B)684 g of sucrose
- (C)90.8 L of dihydrogen at STP
1. (1)C $>$ A $>$ B
2. (2)C $>$ B $>$ A
3. (3)B $>$ C $>$ A
4. (4)B $>$ A $>$ C
We corrected a printing error in the original paper
Answer corrected; the source key is (3) — (A) 2 mol C $_6$ H $_{12}$ = 36 mol atoms, (B) 684 g sucrose = 2 mol = 90 mol atoms, (C) 90.8 L H $_2$ = 4 mol = 8 mol atoms, so B $>$ A $>$ C; also source printed “total number of atoms of present in” and option (4) “B $>$ A C”.
ChemistryJEE Main 5 Apr 2026, Shift 1·Q1·MCQ·Easy–moderate
Open
Stoichiometry of thermal decomposition
How many grams of residue is obtained by heating 2.76 g of silver carbonate ?
(Given : Molar mass of C, O and Ag are 12, 16 and 108 g mol $^{-1}$ respectively)
1. (1)1.08 g
2. (2)2.16 g
3. (3)3.24 g
4. (4)4.32 g
ChemistryJEE Main 5 Apr 2026, Shift 2·Q1·MCQ·Moderate
Open
Limiting reagent gas volume
What volume of hydrogen gas at STP would be liberated by action of 50 mL of $\ce{H2SO4}$ of 50% purity (density $= 1.3$ g mL $^{-1}$ ) on 20 g of zinc ?
Given : Molar mass of H, O, S, Zn are 1, 16, 32, 65 g mol $^{-1}$ respectively.
1. (1)5.824 L
2. (2)7.428 L
3. (3)6.892 L
4. (4)8.375 L
ChemistryJEE Main 6 Apr 2026, Shift 1·Q1·MCQ·Easy–moderate
Open
Empirical formula from composition
An oxide of iron contains 69.9% iron, its empirical formula, is :
(Given : Molar mass of Fe and O are 56 and 16 g mol $^{-1}$ respectively.)
1. (1) $\ce{FeO}$
2. (2) $\ce{Fe2O3}$
3. (3) $\ce{Fe3O4}$
4. (4) $\ce{FeO3}$
ChemistryJEE Main 6 Apr 2026, Shift 2·Q1·MCQ·Easy–moderate
Open
Mole concept number of atoms
Which of the following contain the same number of atoms ?
(Given : Molar mass in g mol $^{-1}$ of H, He, O and S are 1,4,16 and 32 respectively)
- (A)2g of $\ce{O2}$ gas
- (B)4g of $\ce{SO2}$ gas
- (C)1400 mL of $\ce{O2}$ at STP
- (D)0.05 L of He at STP
- (E)0.0625 mol of $\ce{H2}$ gas
Choose the correct answer from the options given below :
1. (1)A and B only
2. (2)B and C only
3. (3)C and D only
4. (4)A, C and E only
We corrected a printing error in the original paper
Source printed “4g fo $\ce{SO2}$ gas”.

ChemistryJEE Main 8 Apr 2026, Shift 2·Q1·MCQ·Easy–moderate

Mole concept number of atoms

Match List-I with List-II.

List-I		List-II
Mass of substance		Number of atoms
A.	1.8 mg water	I.	$2\times10^{-4}\times N_\mathrm{A}$
B.	9.8 mg sulphuric acid	II.	$1.5\times10^{-4}\times N_\mathrm{A}$
C.	1.8 mg carbon	III.	$3\times10^{-4}\times N_\mathrm{A}$
D.	5.85 mg salt (NaCl)	IV.	$7\times10^{-4}\times N_\mathrm{A}$

Choose the correct answer from the options given below :

(1)A-IV, B-III, C-I, D-II
(2)A-III, B-II, C-IV, D-I
(3)A-III, B-IV, C-II, D-I
(4)A-III, B-IV, C-I, D-II