(i) Element X has two valence electrons in M-shell . (ii) In element Y, the electrons are distributed in the first three shells. It has eight electrons in M-shell. (iii) ElementZ has eight electrons in the penultimate shell that is M. Based on the information given in the above three statements, answer the following questions. (a) Give the electronic configuration of X. (b) Which element is stable among X, Y and Z and why ? (c) In which atom of an element is the number of electrons distributed in all four shells ? (d) What is the atomic number of Z in which the number of electrons in the first and the last shell are not the same ? What are the number of electrons and protons present in 'Y' ?

(i) Element X has two valence electrons in M-shell . (ii) In element Y

1.	(i) Element X has two valence electrons in M-shell . (ii) In element Y, the electrons are distributed in the first three shells. It has eight electrons in M-shell. (iii) ElementZ has eight electrons in the penultimate shell that is M. Based on the information given in the above three statements, answer the following questions. (a) Give the electronic configuration of X. (b) Which element is stable among X, Y and Z and why ? (c) In which atom of an element is the number of electrons distributed in all four shells ? (d) What is the atomic number of Z in which the number of electrons in the first and the last shell are not the same ? What are the number of electrons and protons present in 'Y' ?
Answer» Solution :(a) Electronic configuration of X:2 , 8,2 (B) Element Y is STABLE due to the presence of 8 electrons (octet) in the valence SHELL. (c) In the element 'Z', the electrons are distributed in four shells because N-shell `(4^(th))` is the valence shell. (d) Since 8 electrons are present in penultimate shell that is M, 1 electron is present in N-shell because the number of electrons are not the same in K and N shell. Electronic configuration of 'Z' 2,8,8,1 Henceatomic number 'Z'=19. (e) Electronic configuration of Y=2,8,8. HenceZ=18 and the number of protons or electrons are 18.