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How many helium atoms are present in 52u of helium? 

How many helium atoms are present in 52u of helium?  Correct Answer 78.3 × 10<sup>23</sup>

The correct answer is 13.

Concept:

Atomic Number: It is the number of protons or electrons present in the atom.

Mass number:

  • It is the number of protons and neutrons taken together of an atom.
  • It is measured in the atomic mass unit, amu or simply 'u'.

An element is represented in the following manner:

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Explanation:

Mass of 1 He atom = 4 u

4u He has atoms = 1

1u He will have atoms = 1/4

52u He will have atoms = 52/4 = 13

The Number of atoms in 13 moles = 13× 6.022×1023 = 7.8286 × 1024.

Therefore 52 u of He has 7.8286 × 1024 = 78.286 × 1023 atoms.

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