Assertion :The mass of chlorine is 35.5. Reason: Nature chlorine exists in two isotopic forms and these two isotopes have a natural abundance ratio of 3:1.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

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Assertion is correct but Reason is incorrect.

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Both Assertion and Reason are incorrect.

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
Element exists in the form of isotopes in nature. Chlorine is an example of one such element. It is having a fractional atomic mass i.e., 35.5. This is because in nature chlorine exists in two isotopic forms and these two isotopes have a natural abundance ratio of 3:1.
The isotopes of chlorine are: $_{17} C l^{35},_{17} C l^{37}$ and they have an abundance ratio of 3:1.
Average atomic mass= $\frac{75 \times 35 + 37 \times 25}{100} = 35.5$

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(a) Both assertion and reason are correct and the reason is correct explanation of assertion
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(c) Assertion is correct, but reason is incorrect
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