JEE Chemistry 2026 Question with Solution

Given: Reaction is $A + 2B \rightarrow AB_2$. Mass of $A$ is $36.0 \, g$ with molar mass $60 \, g \ mol^{-1}$. Mass of $B$ is $56.0 \, g$ with molar mass $80 \, g \ mol^{-1}$.

Find: Which statements among A, B, C, and D are correct.

Step 1: Calculate moles of reactants

$$n(A) = \frac{36.0}{60} = 0.6 \ \text{mol}$$ $$n(B) = \frac{56.0}{80} = 0.7 \ \text{mol}$$

Step 2: Identify the limiting reagent From

$$A + 2B \rightarrow AB_2$$

$0.6 \, mol$ of $A$ requires

$$2 \times 0.6 = 1.2 \ \text{mol of } B$$

but only $0.7 \, mol$ of $B$ is available. Therefore, $B$ is the limiting reagent, so statement A is false.

Step 3: Calculate amount of product formed From stoichiometry,

$$2 \ \text{mol } B \rightarrow 1 \ \text{mol } AB_2$$

so

$$0.7 \ \text{mol } B \rightarrow 0.35 \ \text{mol } AB_2$$

Molar mass of $AB_2$ is

$$60 + 2(80) = 220 \ \text{g mol}^{-1}$$

Therefore, mass of $AB_2$ formed is

$$0.35 \times 220 = 77.0 \ \text{g}$$

So statement B is correct, and statement C is false because the molar mass is $220 \, g \ mol^{-1}$, not $140 \, g \ mol^{-1}$.

Step 4: Calculate unreacted $A$ Moles of $A$ consumed are

$$0.35 \ \text{mol}$$

Remaining moles of $A$ are

$$0.6 - 0.35 = 0.25 \ \text{mol}$$

Mass of unreacted $A$ is

$$0.25 \times 60 = 15.0 \ \text{g}$$

So statement D is correct.

Conclude: The correct statements are B and D only. Therefore, the correct option is C.

Given: $A + 2B \rightarrow AB_2$

Find: Check each statement individually.

1. Statement A: "$A$ is the limiting reagent."

• Available moles: $n(A)=0.6$ and $n(B)=0.7$.
• Required ratio is $1:2$.
• For $0.6 \, mol$ of $A$, required $B$ is $1.2 \, mol$.
• Since only $0.7 \, mol$ of $B$ is available, $B$ limits the reaction.
• Hence statement A is false.

2. Statement B: "$77.0 \, g$ of $AB_2$ is formed."

• From $0.7 \, mol$ of limiting reagent $B$,

$$\text{moles of } AB_2 = \frac{0.7}{2} = 0.35$$

• Molar mass of $AB_2$ is

$$60 + 2(80) = 220 \ \text{g mol}^{-1}$$

• Product mass is

$$0.35 \times 220 = 77.0 \ \text{g}$$

• Hence statement B is true.

3. Statement C: "Molar mass of $AB_2$ is $140 \, g \ mol^{-1}$."

• Actual molar mass is

$$60 + 160 = 220 \ \text{g mol}^{-1}$$

• Hence statement C is false.

4. Statement D: "$15.0 \, g$ of $A$ is left unreacted after completion of reaction."

• Moles of $A$ consumed with $0.7 \, mol$ of $B$ are

$$\frac{0.7}{2} = 0.35 \ \text{mol}$$

• Remaining $A$ is

$$0.6 - 0.35 = 0.25 \ \text{mol}$$

• Remaining mass is

$$0.25 \times 60 = 15.0 \ \text{g}$$

• Hence statement D is true.

Conclude: Only statements B and D are correct, so the correct option is C.