The atomic number of an element is 31 and the mass number of one of its atoms is 65. This atom contains: a 31 neutrons b 34 protons c 65 protons d 34 neutrons e 34 electrons

d, 34 neutrons

Explanation:

Mass number is the sum of the number of protons and the number of neutrons.

Atomic number equals to the number of protons.

Since the element has an atomic number of 31, it has 31 protons. The number of neutrons equal to mass number - no. of protons,

which in this case is 65 - 31

= 34 neutrons.

In a neutral atom, the no. of electrons equal to the no. of protons, because each proton carries a +1 charge and each  electron carries a -1 charge. To cancel out the charge, their numbers must be equal. So, this atom has 31 electrons.

From the options, only d is correct. (34 neutrons)

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