31. Which one of the following elements will be
an isobar of calcium if the atomic number of
calcium is 20 and its mass number is 40?
A. Element with 20 protons and 18 neutrons
B. Element with 18 protons and 19 neutrons
C. Element with 20 protons and 19 neutrons
D. Element with 18 protons and 22 neutrons
Answers
number of neutrons = 20
An atom of the calcium-40 isotope has 20 neutrons in its nucleus.
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Answer:
(1) The atomic number is equal to the number of protons.
Z
= number of protons
(2) In neutrally charged elements, the number of electrons is the same as the number of protons.
Z
= number of protons = number of electrons (no charge)
Otherwise, positive charge means that the element lost an electron and negative charge means it gained an electron.
(3) The atomic mass is equal to the sum of the number of protons and number of neutrons.
A
= number of protons + number neutrons
or
A
=
Z
+ number neutrons
So if you say that
Z
= 20 and
A
= 40, then
A
=
Z
+ number neutrons
40 = 20 + number of neutrons
40 - 20 = number of neutrons
Therefore,
number of neutrons = 20
Explanation:
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