Chapter Exam

Unit 1: Some Basic Concepts in Chemistry — Online MCQ Test

Q: Taking into account the significant figures, what is the value of 9.99 m - 0.0099 m ?

Answer: A. 9.98 m — In subtraction, the result should have the same number of decimal places as the term with the fewest decimal places. 9.99 has 2 decimal places, and 0.0099 has 4. The result must be rounded to 2 decimal places: 9.99 - 0.0099 = 9.9801, which rounds to 9.98 m.

Q: Dalton's Atomic theory could not explain which of the following?

Answer: D. Law of gaseous volume — Dalton's atomic theory does not account for Gay-Lussac's Law of Gaseous Volumes, which relates to the combining ratios of gases by volume.

Q: Consider the following compounds: KO₂, H₂O₂ and H₂SO₄. The oxidation states of the underlined elements in them are, respectively,

Answer: A. +1, –1, and +6 — In KO₂ (superoxide), K is +1. In H₂O₂, O is –1. In H₂SO₄, S is +6.

Q: Among the following, choose the ones with equal number of atoms. A. 212 g of Na₂CO₃, B. 248 g of Na₂O, C. 240 g of NaOH, D. 12 g of H₂, E. 220 g of CO₂

Answer: B. A, B, and D only — Calculate moles: A=2, B=4, C=6, D=6, E=5. Atoms: A (2*6=12), B (4*3=12), C (6*3=18), D (6*2=12), E (5*3=15). B, D, and E have 12 moles of atoms? No, wait: A(2*6=12 moles of atoms), B(4*3=12 moles of atoms), D(6*2=12 moles of atoms). Actually 12 mol atoms for A, B, D.

Q: Name the class of enzyme that usually catalyze the following reaction: S – G + S# → S + S# – G

Answer: C. Transferase — Enzymes that transfer a group (other than hydrogen) from one substrate to another are classified as transferases.

Q: Which of the following statement about hydrogen is incorrect?

Answer: C. Dihydrogen does not act as a reducing agent — Dihydrogen acts as a reducing agent (e.g., reducing metal oxides). Additionally, Protium is the most common isotope, not Tritium.

Q: 1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution; the mass of sodium hydroxide left unreacted is equal to

Answer: A. Zero mg — Moles of HCl = 0.025 × 0.75 = 0.01875 mol. This neutralizes the same moles of NaOH, i.e. 0.01875 × 40 = 0.75 g = 750 mg. Since 1 g NaOH was given, unreacted NaOH = 250 mg. The correct option is therefore 250 mg.

Q: The highest number of helium atoms is in

Answer: C. 4 mol of helium — Number of atoms is proportional to number of moles. 4 mol contains the maximum number of He atoms among the options.

Q: In which case is the number of molecules of water maximum?

Answer: A. 18 mL of water — Option (a): 18 mL water = 18 g (density ≈1 g/mL) = 1 mol = 6.022×10²³ molecules. Option (b): 10⁻³ mol = 6.022×10²⁰ molecules. Option (c): 0.00224 L at STP = 0.00224/22.4 mol = 10⁻⁴ mol = 6.022×10¹⁹ molecules. Option (d): 0.18 g = 0.01 mol = 6.022×10²¹ molecules. Maximum is option (a): 18 mL of water.

Q: In which case is the number of molecules of water maximum?

Answer: C. 18 mL of water — Option (a): 0.00224 L at STP = 0.00224/22.4 = 10⁻⁴ mol → 10⁻⁴ × 6.022×10²³ ≈ 6.022×10¹⁹ molecules. Option (b): 0.18 g / 18 g/mol = 0.01 mol → 6.022×10²¹ molecules. Option (c): 18 mL water (density ≈ 1 g/mL) = 18 g / 18 g/mol = 1 mol → 6.022×10²³ molecules. Option (d): 10⁻³ mol → 6.022×10²⁰ molecules. Maximum is option (c).

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Unit 1: Some Basic Concepts in Chemistry — Important Questions & Answers (FAQ)

Frequently asked questions from NEET NEET (All) CHEMISTRY — Unit 1: Some Basic Concepts in Chemistry, with answers and explanations. These are sample questions; the exam has its own separate question set.

Taking into account the significant figures, what is the value of 9.99 m - 0.0099 m ?

A. 9.98 m ✓
B. 9.980 m
C. 9.9 m
D. 9.9801 m

Answer: A. 9.98 m
In subtraction, the result should have the same number of decimal places as the term with the fewest decimal places. 9.99 has 2 decimal places, and 0.0099 has 4. The result must be rounded to 2 decimal places: 9.99 - 0.0099 = 9.9801, which rounds to 9.98 m.

Dalton's Atomic theory could not explain which of the following?

A. Law of conservation of mass
B. Law of constant proportion
C. Law of multiple proportion
D. Law of gaseous volume ✓

Answer: D. Law of gaseous volume
Dalton's atomic theory does not account for Gay-Lussac's Law of Gaseous Volumes, which relates to the combining ratios of gases by volume.

Consider the following compounds: KO₂, H₂O₂ and H₂SO₄. The oxidation states of the underlined elements in them are, respectively,

A. +1, –1, and +6 ✓
B. +2, –2, and +6
C. +1, –2, and +4
D. +4, –4, and +6

Answer: A. +1, –1, and +6
In KO₂ (superoxide), K is +1. In H₂O₂, O is –1. In H₂SO₄, S is +6.

Among the following, choose the ones with equal number of atoms. A. 212 g of Na₂CO₃, B. 248 g of Na₂O, C. 240 g of NaOH, D. 12 g of H₂, E. 220 g of CO₂

A. A, B, and C only
B. A, B, and D only ✓
C. B, C, and D only
D. B, D, and E only

Answer: B. A, B, and D only
Calculate moles: A=2, B=4, C=6, D=6, E=5. Atoms: A (2*6=12), B (4*3=12), C (6*3=18), D (6*2=12), E (5*3=15). B, D, and E have 12 moles of atoms? No, wait: A(2*6=12 moles of atoms), B(4*3=12 moles of atoms), D(6*2=12 moles of atoms). Actually 12 mol atoms for A, B, D.

Name the class of enzyme that usually catalyze the following reaction: S – G + S# → S + S# – G

A. Hydrolase
B. Lyase
C. Transferase ✓
D. Ligase

Answer: C. Transferase
Enzymes that transfer a group (other than hydrogen) from one substrate to another are classified as transferases.

Which of the following statement about hydrogen is incorrect?

A. Hydrogen never acts as cation in ionic salts
B. Hydronium ion, H3O+ exists freely in solution
C. Dihydrogen does not act as a reducing agent ✓
D. Hydrogen has three isotopes of which tritium is the most common

Answer: C. Dihydrogen does not act as a reducing agent
Dihydrogen acts as a reducing agent (e.g., reducing metal oxides). Additionally, Protium is the most common isotope, not Tritium.

1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution; the mass of sodium hydroxide left unreacted is equal to

A. Zero mg ✓
B. 200 mg
C. 750 mg
D. 250 mg

Answer: A. Zero mg
Moles of HCl = 0.025 × 0.75 = 0.01875 mol. This neutralizes the same moles of NaOH, i.e. 0.01875 × 40 = 0.75 g = 750 mg. Since 1 g NaOH was given, unreacted NaOH = 250 mg. The correct option is therefore 250 mg.

The highest number of helium atoms is in

A. 4 g of helium
B. 2.271098 L of helium at STP
C. 4 mol of helium ✓
D. 4 u of helium

Answer: C. 4 mol of helium
Number of atoms is proportional to number of moles. 4 mol contains the maximum number of He atoms among the options.

In which case is the number of molecules of water maximum?

A. 18 mL of water ✓
B. 10⁻³ mol of water
C. 0.00224 L of water vapours at 1 atm and 273 K
D. 0.18 g of water

Answer: A. 18 mL of water
Option (a): 18 mL water = 18 g (density ≈1 g/mL) = 1 mol = 6.022×10²³ molecules. Option (b): 10⁻³ mol = 6.022×10²⁰ molecules. Option (c): 0.00224 L at STP = 0.00224/22.4 mol = 10⁻⁴ mol = 6.022×10¹⁹ molecules. Option (d): 0.18 g = 0.01 mol = 6.022×10²¹ molecules. Maximum is option (a): 18 mL of water.

In which case is the number of molecules of water maximum?

A. 0.00224 L of water vapours at 1 atm and 273 K
B. 0.18 g of water
C. 18 mL of water ✓
D. 10⁻³ mol of water

Answer: C. 18 mL of water
Option (a): 0.00224 L at STP = 0.00224/22.4 = 10⁻⁴ mol → 10⁻⁴ × 6.022×10²³ ≈ 6.022×10¹⁹ molecules. Option (b): 0.18 g / 18 g/mol = 0.01 mol → 6.022×10²¹ molecules. Option (c): 18 mL water (density ≈ 1 g/mL) = 18 g / 18 g/mol = 1 mol → 6.022×10²³ molecules. Option (d): 10⁻³ mol → 6.022×10²⁰ molecules. Maximum is option (c).

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Unit 2: Atomic Structure