1.

Chlorine occurs in nature in two isotopic forms of masses 35 u and 37 u in the ratio of 3 ∶ 1 respectively. What is the average atomic mass of the Chlorine atom ?1. 36.1 u2. 35.5 u3. 36.5 u4. 35.1 u

Answer» Correct Answer - Option 2 : 35.5 u

  • Explanation:
    • The average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element.
    • To find the average atomic mass of an atom, we take into account all of the isotopes that exist and the percentage of each type.
    • Average atomic mass = (Mass of isotope × Relative abundance).
    • The isotopes of chlorine, found in nature are in the ratio 3 : 1.
  • Calculation:
    • Given:
    • Isotopic forms of masses 35 u and 37 u
    • The average atomic mass of chlorine 

\(M=(35 \times \frac{75}{100})+(37 \times \frac{25}{100})\)

\(M=\frac{105}{4}+\frac{37}{4}\)

\(M=\frac{142}{4}\)

M = 35.5 u 

The average atomic mass of chlorine is equal to 35.5 u.​


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