An atom of an element X may be written as ${}_{4}^{9}X$ .
(a) What does the figure 9 indicate?

(b) What does the figure 4 indicate?

(c) What is the number of protons in atom X?

(d) What is the number of neutrons in atom X?

(e) What is the number of electrons in atom X?

(f) How many electrons are there in the outermost shell of an atom of element X?

(g) Write the symbol of ion formed by an atom of element X.

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Solution

(a) Figure 9 indicates the mass number.
(b) Figure 4 indicates the atomic number.
(c) No. of protons in atom X = 4
(d) No. of neutrons in atom X = 9 – 4 = 5
(e) No. of electrons in atom X = 4
(f) Electrons in the outermost shell of an atom of element X = 2
(g) X²⁺

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(a) Figure 9 indicates the mass number. (b) Figure 4 indicates the atomic number. (c) No. of protons in atom X = 4 (d) No. of neutrons in atom X = 9 – 4 = 5 (e) No. of electrons in atom X = 4 (f) Electrons in the outermost shell of an atom of element X = 2 (g) X2+

(a) Figure 9 indicates the mass number.
(b) Figure 4 indicates the atomic number.
(c) No. of protons in atom X = 4
(d) No. of neutrons in atom X = 9 – 4 = 5
(e) No. of electrons in atom X = 4
(f) Electrons in the outermost shell of an atom of element X = 2
(g) X²⁺