Question

An atom of an element has one electron in the valence shell. It can be represented as :

• A. ${}_6{A}^{12}$
• B. ${}_{19}{A}^{39}$
• C. ${}_{13}{A}^{27}$
• D. ${}_{12}{A}^{24}$

Answer 1

The correct option is B ${}_{19}{A}^{39}$

The atomic no. of $A_6^{12}$ is 6. Its electronic configuration is $1s^{2}2s^{2}2p^2$. It has 4 electrons in valence shell.

The atomic no. of $A_{19}^{39}$ is 19. Its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^1$. It has 1 electron in valance shell.

The atomic no. of $A_{13}^{27}$ is 13. Its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^1$. It has 3 electrons in valence shell.

The atomic no. of $A_{12}^{24}$ is 12. Its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^2$. It has 2 electrons in valence shell.

Therefore, the correct answer is option B.