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Question

Which of the following contains the largest number of atoms?


A

11gofCO2

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B

4gofH2

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C

5gofNH3

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D

8gofSO2

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Solution

The correct option is B

4gofH2


The explanation for the correct option:

(B) 4gofH2

Step 1: Calculation of the number of moles

  • Number of moles (n) =wM

Where,

w is the given weight of the compound in grams

M is the molar mass of the compound

  • Number of moles in 4gofH2 =42mol

=2mol

Step 2: Calculation of the number of molecules

  • Number of molecules =n×NA

Where,

NA is Avogadro's number which is equal to 6.022×1023molecules

  • Number of molecules in 4gofH2 =2×6.022×1023molecules

=12.044×1023 molecules

Step 3: Calculation of the number of atoms

  • Number of atoms in one molecule of Hydrogen gas =2atoms
  • Number of atoms in 12.044×1023 molecules of Hydrogen gas =2×12.044×1023atoms

=24.088×1023 atoms

  • Therefore, it has the maximum number of atoms and is the correct answer.

The explanation for the incorrect options:

(A) 11gofCO2

Step 1: Calculation of the number of moles

  • Number of moles (n) =wM

Where,

w is the given weight of the compound in grams

M is the molar mass of the compound

  • Number of moles in 11gofCO2 =1144mol

=0.25mol

Step 2: Calculation of the number of molecules

  • Number of molecules =n×NA

Where,

NA is Avogadro's number which is equal to 6.022×1023molecules

  • Number of molecules in 11gCO2 =0.25×6.022×1023molecules

=1.505×1023 molecules

Step 3: Calculation of the number of atoms

  • Number of atoms in one molecule of Carbon dioxide =3atoms
  • Number of atoms in 1.505×1023 molecules of Carbon dioxide =3×1.505×1023atoms

=4.516×1023 atoms

  • Therefore, it does not have the maximum number of atoms and is the incorrect answer.

(C) 5gofNH3

Step 1: Calculation of the number of moles

  • Number of moles (n) =wM

Where,

w is the given weight of the compound in grams

M is the molar mass of the compound

  • Number of moles in 5gofNH3 =517

=0.2941mol

Step 2: Calculation of the number of molecules

  • Number of molecules =n×NA

Where,

NA is Avogadro's number which is equal to 6.022×1023molecules

  • Number of molecules in 5gNH3 =0.2941×6.022×1023molecules

=1.771×1023 molecules

Step 3: Calculation of the number of atoms

  • Number of atoms in one molecule of Ammonia =4atoms
  • Number of atoms in 1.771×1023 molecules of Ammonia =4×1.771×1023atoms

=7.084×1023 atoms

  • Therefore, it does not have the maximum number of atoms and is the incorrect answer.

(D) 8gofSO2

Step 1: Calculation of the number of moles

  • Number of moles (n) =wM

Where,

w is the given weight of the compound in grams

M is the molar mass of the compound

  • Number of moles in 8gofSO2 =864

=0.125mol

Step 2: Calculation of the number of molecules

  • Number of molecules =n×NA
  • Where,NA is Avogadro's number which is equal to 6.022×1023molecules
  • Number of molecules in 8gSO2 =0.125×6.022×1023molecules

=0.752×1023 molecules

Step 3: Calculation of the number of atoms

  • Number of atoms in one molecule of Sulphur dioxide =3atoms
  • Number of atoms in 0.752×1023 molecules of Sulphur dioxide =3×0.752×1023atoms

=2.258×1023 atoms

  • Therefore, it does not have the maximum number of atoms and is the incorrect answer.

Hence, the correct option is (B) 4gofH2.


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