Assertion :Actual atomic mass is greater than mass number. Reason: Mass of protons and neutrons is measured in daltons or atomic mass unit (u) but the mass of each neutron and proton is slightly greater than 1 dalton.

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
Mass number = number of protons + number of neutrons in an atom.
Now, mass of protons and neutrons is measured in daltons or atomic mass unit,u but the mass of each neutron and proton is slightly greater than 1 dalton, so actual atomic mass is slightly greater than mass number.
Example:
mass number of calcium = 20 + 20 = 40 u
Actual atomic mass of calcium = 40.078 u

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