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Physics

A certain nucleus P has a mass number 15 and atomic number 7.

(a) Find the number of neutrons.

(b) Write the symbol for the nucleus P.

(c) Write the symbols of the resulting nuclei in the following cases if :
the nucleus P loses :

  1. one proton
  2. one B-particle
  3. one α-particle

Express each change by a reaction.

Radioactivity

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Answer

(a) The number of neutrons in a nucleus can be calculated using the formula:

Number of neutrons = Mass number (A) - Atomic number (Z)

Given,

Mass number (A) = 15
Atomic number (Z) = 7
So, number of neutrons = 15 - 7 = 8

(b) The nucleus P can be written as 157P.

(c)

  1. After the loss of 1 proton, the mass number and atomic number of the nucleus P will decrease by 1.The new nucleus will be 614Q^{14}6\text Q (say). The change can be written as :
    715P → 614Q + 11p^{15}7\text P \ → \ ^{14}6\text Q \ + \ ^{1}1\text p

  2. After the loss of one β particle, the mass number will remain the same, but the atomic number will increase by 1. The nucleus 715P^{15}7\text P changes to 815R^{15}8\text R (say) as follows :

715P → 815R + −10e^{15}7\text P \ → \ ^{15}8\text R \ + \ ^{0}_{-1}\text e

  1. After the loss of one α particle, the mass number decreases by 4 and the atomic number decreases by 2. The nucleus 715P^{15}7\text P changes to 811S^{11}8\text S (say) as follows :

715P → 511S + 24He^{15}7\text P \ → \ ^{11}5\text S \ + \ ^{4}_2\text {He}

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