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: 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.

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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.

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.