GK
CHEMISTRY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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It has 9 neutrons in its nucleus.
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It is an isotope of oxygen.
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Its atomic mass is a decimal number.
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It cannot be an atom of oxygen.
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Detailed explanation-1: -Expert Answer The correct answer is option D. The Oxygen (O) has an atomic number of 8 and has a mass number of 16. Upon accepting 2 electrons it becomes O2-. The mass number is defined as the sum of the number of protons and neutrons present in the molecule.
Detailed explanation-2: -Oxygen atom has 8 electrons, 8 protons and 8 neutrons.
Detailed explanation-3: -Oxygen is group 8 element, so, the atom of oxygen has 8 protons and 8 electrons. The ion has the same number of protons because you never lose a proton to make an ion. But in the case of oxide form, it carries two negative charges. Negative charge come due to the transfer of electron.
Detailed explanation-4: -Thus, since this element has 8 protons, its atomic number is 8 (oxygen). Since the question also lists the number of neutrons, we can determine the mass number of this element to be 17. The notation for this isotope of oxygen would be 178 O.