There are 2, 8, and 7 electrons in the shells K, L, and M, respectively. If the mass number of the atom is 37, what is the number of neutrons? [1 mark]

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Solution

We can calculate atomic number by adding the number of electrons in all the shells and then subtracting it from the mass number, to get the value of number of neutrons.

Given:
Mass number: 37
Electronic configuration: 2, 8, 7
So, atomic number will be: 17 (2+8+7) [0.5 mark]

Now, the number of neutrons = Mass no. - Atomic no.
=> 37 - 17= 20 [0.5 mark]

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Q. There are 2,8 and 7 electrons in the shells K,L and M, respectively. If the mass number of the atom is 37, What is the number of neutrons?

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Q. Number of electrons and neutrons in an atom are 6 and 8 respectively. What is the mass number of the atom?

Q. An element has atomic number

17

and mass number

37

. There are

17

electrons outside the nucleus. Find the number of neutrons in it.

Q. Answer the following questions:
(A) Explain Isotopes, Isobars and Isotones along with examples. [3 Marks]

(B) The atomic composition of element A is as follows: number of neutrons = x, atomic mass = 12, number of electrons = 6. The atomic composition of B is as follows: number of neutrons = y, atomic mass = 28, number of electrons = number of electrons in A + 8. Compute the ratio of x to y. [2 Marks]

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