An atom of element X has 17 protons. How many electrons are present in its valence shell?

• A. 8
• B. 7
• C. 1
• D. 5

Answer: (B)

Verified step by step guidance

1. Identify the element based on the number of protons. Since the atom has 17 protons, it corresponds to the element with atomic number 17, which is chlorine (Cl).
2. Recall the electron configuration for chlorine. The total number of electrons equals the number of protons in a neutral atom, so chlorine has 17 electrons.
3. Write the electron configuration by filling the energy levels in order: 1s, 2s, 2p, 3s, and 3p orbitals.
4. Determine the electrons in the valence shell, which is the outermost shell. For chlorine, the valence shell is the third shell (n=3), which includes the 3s and 3p orbitals.
5. Count the electrons in the 3s and 3p orbitals to find the number of valence electrons. This will give the number of electrons present in the valence shell.