Question

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​

Answer 1

Isobar:

The atoms of different elements having the same mass number but different atomic numbers are called isobars.

Answer:

D.Element with 18 proton and 22 neutron.

Reason:

A = 22 + 18 = 40 and Z = 18. Therefore having same atomic mass but different atomic no.

Answer 2

Need to find:

• The isobar of calcium.

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Knowledge Required:

What's an isobar?

▪ Atoms of different elements having the same mass number are called isobars.

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Ans:

• Option D is correct

Element with 18 protons and 22 neutrons

Explanation:

Here

The Mass number = Z= Number of neutrons+ Number of protons

⟹ Z = 22 + 18

⟹$\purple{\bold{ Z = 40}}$

Also given the mass number of Calcium = 40

Now atomic number of given element = 18

And atomic number of Calcium = 20

Thus as the Mass numbers of the two are same and their atomic numbers are different so they are isobars.

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Check other options :

• A. Element with 20 protons and 18 neutrons

Here Z = 38 which isn't equal to calcium thus it's not an isobar of calcium

• B. Element with 18 protons and 19 neutrons

Here Z = 37 which isn't equal to calcium thus it's also not an isobar of calcium

• C. Element with 20 protons and 19 neutrons

Here Z = 39 which isn't equal to calcium thus it's also not an isobar of calcium

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Thus $\red{\bold{\large{\boxed{ Option \: D\: is \: Correct }}}}$