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Some Basic Concepts of Chemistry question

2020 · 6 Sep · Shift 2 · Q2
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Some Basic Concepts of Chemistry question

2020 · 6 Sep · Shift 2 · Q2

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1
The average molar mass of chlorine is 35.5 g mol–1. The ratio of 35Cl to 37Cl in naturally occuring chlorine is close to :
  1. A
    1 : 1
  2. B
    2 : 1
  3. C
    3 : 1
  4. D
    4 : 1
View written solutionFree

Correct answer: C

  1. Let the fraction of 35Cl^{35}\text{Cl}35Cl be xxx and the fraction of 37Cl^{37}\text{Cl}37Cl be (1−x)(1-x)(1−x).

  2. The average molar mass is the weighted average:

35x+37(1−x)=35.535x + 37(1-x) = 35.535x+37(1−x)=35.5

  1. Solve:

35x+37−37x=35.535x + 37 - 37x = 35.535x+37−37x=35.5 37−2x=35.537 - 2x = 35.537−2x=35.5 2x=1.52x = 1.52x=1.5 x=0.75x = 0.75x=0.75

So,

  • fraction of 35Cl=0.75^{35}\text{Cl} = 0.7535Cl=0.75
  • fraction of 37Cl=0.25^{37}\text{Cl} = 0.2537Cl=0.25
  1. Therefore, the ratio is:

35Cl:37Cl=0.75:0.25=3:1^{35}\text{Cl} : ^{37}\text{Cl} = 0.75 : 0.25 = 3 : 135Cl:37Cl=0.75:0.25=3:1

  1. Checking options:
  • A: 1:11:11:1 ❌
  • B: 2:12:12:1 ❌
  • C: 3:13:13:1 ✅
  • D: 4:14:14:1 ❌

Hence, the correct answer is C.

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