Question 1

1. How many significant figures are present in the measurement 0.0025 g?

A) 1B) 2C) 3D) 4

Answer

✓ Correct Answer: Option B

Explanation: Explanation: Leading zeros acting as placeholders before the first non-zero digit are not significant. Only the non-zero integer digits 2 and 5 are significant. Thus, the total count is 2.

Question 2

2. What is the standard scientific notation expression representing the number 450,000?

A) $4.5 \times 10^5$B) $45 \times 10^4$C) $4.5 \times 10^{-5}$ $0.45 \times 10^6$

Question 3

3. Calculate the standard molar mass of Methane ($CH_4$). (Atomic mass constants: C = 12.01, H = 1.008)

A) 13.018 g/molB) 14.04 g/molC) 16.04 g/molD) 18.02 g/mol

Answer

✓ Correct Answer: Option C

Explanation: Solution: $$Molar Mass = 1 \times (12.01) + 4 \times (1.008) = 12.01 + 4.032 = 16.042 g/mol$$ Rounding cleanly down to two decimal places yields 16.04 g/mol.

Question 4

4. One mole of water ($H_2O$) molecules contains precisely how many individual molecules?

A) $6.022 \times 10^{23}$B) $3.011 \times 10^{23}$C) $1.204 \times 10^{24}$D) $6.022 \times 10^{22}$

Answer

✓ Correct Answer: Option A

Explanation: Explanation: By chemical definition, 1 mole of any pure elementary substance contains Avogadro's constant number of particles: $N_A = 6.022 \times 10^{23}$.

Question 5

5. Which of the following units defines the official SI base unit tracking the amount of substance?

A) KilogramB) GramC) LiterD) Mole

Answer

✓ Correct Answer: Option D

Explanation: Explanation: The International System of Units (SI) defines the **mole** (symbol: mol) as the base foundational measurement unit for aggregate amount of substance.

Question 6

6. What is the net mass of 2.0 moles of Carbon Dioxide ($CO_2$)? (Molar mass of $CO_2 = 44 g/mol$)

A) 44 gB) 88 gC) 22 gD) 100 g

Answer

✓ Correct Answer: Option B

Explanation: Solution: $$Mass = moles \times molar mass = 2.0 mol \times 44 g/mol = 88 g.$$

Question 7

7. Calculate the mass percentage of Oxygen inside standard Water ($H_2O$). (Molar mass references: $H_2O = 18 g/mol$, O = 16 g/mol)

A) 88.89%B) 11.11%C) 50.00%D) 16.00%

Answer

✓ Correct Answer: Option A

Explanation: Solution: $$Mass % = \left( \frac{Mass of O component}{Total molar mass of H_2O} \right) \times 100 = \left( \frac{16}{18} \right) \times 100 \approx 88.89%.$$

Question 8

8. Which pioneering chemical scientist is credited with establishing the Law of Conservation of Mass?

A) John DaltonB) Joseph ProustC) Antoine LavoisierD) Gay-Lussac

Answer

✓ Correct Answer: Option C

Explanation: Explanation: Antoine Lavoisier formulated the fundamental Law of Conservation of Mass, establishing experimentally that mass is neither created nor destroyed during the course of an isolated chemical reaction.

Question 9

9. What is the empirical formula representation of Benzene ($C_6H_6$)?

A) $C_2H_2$B) CHC) $C_3H_3$D) $C_6H_6$

Answer

✓ Correct Answer: Option B

Explanation: Explanation: The empirical formula profiles the simplest, irreducible whole-number integer ratio of atoms. For molecular formula $C_6H_6$, the subscript ratio 6:6 reduces down structurally to 1:1, yielding formula CH.

Question 10

10. Molarity (M) concentration is formally defined as the total number of moles of solute dissolved within:

A) 1 Liter of solutionB) 1 Kilogram of solventC) 1 Liter of solventD) 1 mole of solute

Answer

✓ Correct Answer: Option A

Explanation: Explanation: Molarity is a volumetric concentration parameter defined strictly as the absolute number of moles of solute contained per single Liter (1 L) of the total combined volumetric solution space.

Accepted Answer

✓ Correct Answer: Option A

Explanation: Explanation: Shift the reference decimal point 5 positions leftward: 450,000.0 \rightarrow 4.5. Because the positional progression tracks leftward, the tracking exponential exponent factor is positive: $4.5 \times 10^5$.

Grade 11 : Chemistry - Basic Concepts (Set 1)

1. How many significant figures are present in the measurement 0.0025 g?

2. What is the standard scientific notation expression representing the number 450,000?

3. Calculate the standard molar mass of Methane ($CH_4$). (Atomic mass constants: C = 12.01, H = 1.008)

4. One mole of water ($H_2O$) molecules contains precisely how many individual molecules?

5. Which of the following units defines the official SI base unit tracking the amount of substance?

6. What is the net mass of 2.0 moles of Carbon Dioxide ($CO_2$)? (Molar mass of $CO_2 = 44 g/mol$)

7. Calculate the mass percentage of Oxygen inside standard Water ($H_2O$). (Molar mass references: $H_2O = 18 g/mol$, O = 16 g/mol)

8. Which pioneering chemical scientist is credited with establishing the Law of Conservation of Mass?

9. What is the empirical formula representation of Benzene ($C_6H_6$)?

10. Molarity (M) concentration is formally defined as the total number of moles of solute dissolved within: