Some Basic Concepts of Chemistry

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Some Basic Concepts of Chemistry — solved practice questions

8 NEET Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   The number of moles present in 5.85 g of sodium chloride (molar mass = 58.5 g/mol) is:

   • A1 mol
   • B0.1 mol
   • C0.01 mol
   • D10 mol
   Show answer & solution

   Correct answer: (B) 0.1 mol

   Moles = mass / molar mass = 5.85 / 58.5 = 0.1 mol.

2. Q2easy

   How many molecules are present in 0.5 mole of carbon dioxide? (Avogadro number = 6.022 x 10^23 per mol)

   • A6.022 x 10^23
   • B1.204 x 10^24
   • C3.011 x 10^23
   • D1.505 x 10^23
   Show answer & solution

   Correct answer: (C) 3.011 x 10^23

   Number of molecules = moles x Avogadro number = 0.5 x 6.022 x 10^23 = 3.011 x 10^23.

3. Q3easy

   The percentage by mass of oxygen in water (H2O) is approximately:

   • A11.1%
   • B50%
   • C66.6%
   • D88.9%
   Show answer & solution

   Correct answer: (D) 88.9%

   Mass of O / mass of H2O x 100 = 16 / 18 x 100 = 88.9%.

4. Q4medium

   The molarity of a solution prepared by dissolving 4 g of NaOH (molar mass = 40 g/mol) in enough water to make 250 mL of solution is:

   • A0.4 M
   • B0.1 M
   • C1.0 M
   • D0.04 M
   Show answer & solution

   Correct answer: (A) 0.4 M

   Moles NaOH = 4/40 = 0.1 mol; Molarity = 0.1 mol / 0.250 L = 0.4 M.

5. Q5medium

   A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is: (atomic masses: C=12, H=1, O=16)

   • ACHO
   • BCH2O
   • CC2H4O2
   • DCH4O
   Show answer & solution

   Correct answer: (B) CH2O

   Mole ratio C:H:O = 40/12 : 6.7/1 : 53.3/16 = 3.33 : 6.7 : 3.33 = 1 : 2 : 1, so empirical formula is CH2O.

6. Q6medium

   The mass of 3.011 x 10^23 atoms of carbon (atomic mass = 12 u) is:

   • A12 g
   • B3 g
   • C6 g
   • D24 g
   Show answer & solution

   Correct answer: (C) 6 g

   Moles = 3.011 x 10^23 / 6.022 x 10^23 = 0.5 mol; mass = 0.5 x 12 = 6 g.

7. Q7medium

   The volume occupied by 0.25 mole of an ideal gas at STP (molar volume = 22.4 L/mol) is:

   • A22.4 L
   • B11.2 L
   • C2.24 L
   • D5.6 L
   Show answer & solution

   Correct answer: (D) 5.6 L

   Volume = moles x molar volume = 0.25 x 22.4 = 5.6 L.

8. Q8hard

   Which of the following has the largest number of atoms? (atomic/molar masses: H=1, He=4, C=12, O=16)

   • A1 g of H2
   • B1 g of He
   • C1 g of CH4
   • D1 g of O2
   Show answer & solution

   Correct answer: (A) 1 g of H2

   1 g H2 = 0.5 mol = 1 mol atoms (6.022 x 10^23 atoms); 1 g He = 0.25 mol = 0.25 mol atoms; 1 g CH4 (16 g/mol) = 0.0625 mol x 5 atoms = 0.3125 mol atoms; 1 g O2 = 0.03125 mol x 2 = 0.0625 mol atoms. Hydrogen gas has the most atoms.

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