# Selina Solutions Class 9 Chemistry Solutions for Exercise 4C in Chapter 4 - Chapter 4 Atomic Structure And Chemical Bonding

Question 7 Exercise 4C

\frac{24}{12} M g \text { and } \frac{26}{12} M g \text { are symbols of two isotopes of magnesium }

(a) Compare the atoms of these isotopes with respect to :

(i) the composition of their nuclei.

(ii)their electronic configurations.

(b) Give reasons why the two isotopes of magnesium have different mass numbers

Hence, composition of nuclei

12 \mathrm{Mg}^{24} \rightarrow\left[\begin{array}{cc} \mathrm{p} & \mathrm{n} \\ 12 & +12 \end{array}\right]+2^{\mathrm{Mg}^{26}} \quad,\left[\begin{array}{ccc} \mathrm{p} & \mathrm{n} \\ 12 & +14 \end{array}\right]

ii). Electronic configuration = 2, 8, 2

b) Mass numbers of isotopes of Magnesium are different because of the different number of neutrons, i.e. 12 and

14, respectively.

Video transcript
"hello everyone welcome to leader learning i am gurpreet your science tutor today's question is 2412 mg and 2612 mg are the symbols of two isotopes of magnesium first a part that is compare the atoms of these isotopes with respect to composition of the nuclei second their electronic configurations and b part give reason why the two isotopes of magnesium have different mass numbers right so let us discuss first the composition that is the first part here the two symbols have been given mg 1224 and mg 12 26 right so here proton and electron will be equals to the atomic number that is 12 and here also proton and electron that equals to 12 neutron here will be also 12 because 24 minus 12 is 12 only and neutron here will be 26 minus 12 that is 40. so this is the composition for the both of the nucleis of magnesium second the electronic configuration atomic numbers are say same in both those cases so its electronic configuration will be 2 8 2 this will be the electronic configuration now the question is asking the reason behind the two isotopes of magnesium have different mass numbers because here the neutrons in both isotopes isotopes are different so the mass number is also is different right for more such videos please subscribe leader learning and for any doubts drop a comment thank you "
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