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Assertion. Average atomic mass of an ele...

Assertion. Average atomic mass of an element depends mainly on the heavier isotope.
Reason. Average atomic mass is obtained by multiplying the atomic mass of the heavier isotops with its fractional abundance.

A

If both assertion and reason are true, and reason is the true explanation of the assertion.

B

If both assertion and reason are true, but reason is not the true explanation of the assetion.

C

If assertion is true, but reason if false

D

If both assertion and reason are false.

Text Solution

Verified by Experts

The correct Answer is:
D
Correct A. Average atomic mass depends upon the atomic masses of different isotopes and their fractional abundances.
Correct R. It is obtained by multiplying atomic masses of the isotopes with their corresponding fractional abundances and then adding.
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Calculation of average atomic mass: The atomic attoms fo the two stbale isopes of boron, ._(5)^(10)B (19.78%) and ._(11)^(5)B (80.22%) , are 10.0129 u and 11.0093 u , respectively, Calculate the average atomic mass of boron. Strategy : The atomic mass of an element existing in nature as istopes is the weighted average of the istope masses, Thus, multiply the fracton of each isotope by its mass and add these numbers to obtain the mass of born.

An atom of an element is 13 times heavier than the mass of a carbon atom. What is its mass in a.m.u. ?

Knowledge Check

  • The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence. An element occurs in two isotopic forms with atomic masses 10 and 11. What is the percentage abundance of two isotopes in the sample having atomic mass 10.80?

    A
    20,80
    B
    50,50
    C
    25,70
    D
    60, 40

  • The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence. The fractional atomic masses of elements are due to the existence of

    A
    isotopes having different masses
    B
    diagonal relationship
    C
    equal number of electrons and protons
    D
    none of these.

  • The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence. Chlorine occurs in nature in the form of two isotopes with atomic masses 35 u and 37 u in the ratio of 3 : 1 respectively. Atomic mass of chlorine is

    A
    35.5 u
    B
    34.5 u
    C
    35 u
    D
    36 u

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    Assertion. Atomic mass of sodium is 23 u. Reason. An atom of sodium is 23 times heavier than an atom of carbon-12 isotope.

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