Which one of the following is the average atomic mass of chlorine atom

Which one of the following is the average atomic mass of chlorine atom ?

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35.9 u

35.5 u

35.0 u

37.0 u

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Answer is Wrong!

This question was previously asked in

UPSC CAPF – 2020

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The average atomic mass of chlorine atom is approximately 35.5 u.

Chlorine occurs naturally as a mixture of two main isotopes: chlorine-35 (³⁵Cl) and chlorine-37 (³⁷Cl). Their approximate natural abundances are about 75% for ³⁵Cl (mass ≈ 34.97 u) and 25% for ³⁷Cl (mass ≈ 36.97 u). The average atomic mass is a weighted average of the masses of its isotopes based on their natural abundance.

Average atomic mass = (0.75 × 34.97 u) + (0.25 × 36.97 u) ≈ 26.23 u + 9.24 u ≈ 35.47 u, which is rounded to 35.5 u.

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