Which pair below describes isotopes of the same element? a) an atom with 6 protons and 8 neutrons - an atom with 8 protons and 6 neutrons b) an atom with 6 protons and 6 neutrons - an atom with 6 protons and 7 neutrons c) an atom with 8 protons and 8 neutrons - an atom with 7 protons and 8 neutrons d) an atom with 7 protons and 6 neutrons - an atom with 6 protons and 6 neutrons

B)an atom with 6 protons and 6 neutrons - an atom with 6 protons and 7 neutrons

Explanation:

Isotopes are elements which have same atomic number but different mass number.

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Thus isotopes of same element must have same number of protons and different number of neutrons.

The only combination that fulfil this criteria is : an atom with 6 protons and 6 neutrons - an atom with 6 protons and 7 neutrons

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000

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